University of California

Soils

Anthony T. O’Geen and Kerry Arroues

Classifying Soils and Land

Soil Classification

Researchers and managers like to organize the world they live in so that they can explain their environment.  Soil scientists have developed soil taxonomy procedures to help them classify soils and to understand soil similarities and differences.   Plant ecologists and range scientists have developed several vegetation classification methods (see Ecology Chapter) and USDA Natural Resources Conservation Service (NRCS) has classified land with similar vegetation and soils into ecological sites.

Using the USDA Soil Taxonomy soils can be classified to several levels:  Order, Suborder, Great Group, Subgroup, Family, and Series.  There are 12 soil orders but not all occur on rangelands.  Soil orders are frequently defined by a single dominant characteristic affecting soils in that location, e.g., the prevalent vegetation (Mollisols, Histosols), the type of parent material (Andisols, Vertisols),  the climate variables such as lack of precipitation (Aridisols) or the presence of permafrost (Gelisols).  Also significant in several soil orders is the amount of physical and chemical weathering present (Oxisols, Ultisols, Alfisols, Inceptisols, Entisols), and/or the relative amount of soil profile development that has taken place.  These soil orders can be subdivided into suborders and great groups.  In California most annual rangeland soils fall into 5 Great Groups:  Haploxerolls, Haploxeralfs, Xerorthents, Argixerolls, and Haploxererts.  The soil series is the lowest taxonomic class and consists of soils within a family that have horizons similar in color, texture, structure, reaction, consistence, mineral composition, and arrangement in the profile. There are more than 100 soil series in the annual rangelands (Table 1).  Great Soils Groups and example soil series of the Coast Range and Sierra Nevada foothills will be describe in this chapter.

Major Land Resource Areas

USDA NRCS has organized the United States into “Major Land Resource Areas (MLRA).”  Major Land Resource Areas can be subdivided into ecological sites.  An ecological site is a kind of land with a specific potential natural community and specific physical site characteristics, differing from other kinds of land in its ability to produce vegetation and to respond to management.  Soil characteristics, precipitation, elevation, and aspect play significant roles in determining the kind and amount of vegetation produced. This chapter will primarily focus on soil characteristics on MLRA 15 along the coast (Figure 1) and MLRA 18 along the Sierra Nevada Foothills (Figure 2).  Annual rangeland also occurs on the edge of the Sacramento and San Joaquin Valleys (MLRA 17, Figure 3) and the Southern California Mountains (MLRA 20, Figure 4).

Figure 1. Major Land Resource Area 15
Figure 1. Major Land Resource Area 15

Figure 2.  Major Land Resource Area 18
Figure 2. Major Land Resource Area 18

Figure 3.  Major Land Resource Area 17
Figure 3. Major Land Resource Area 17

Figure 4.  Major Land Resource Area 20
Figure 4. Major Land Resource Area 20

In this chapter we will briefly discuss soil formation.  We will then focus on the characteristics of soils in the Coast Range and in the Sierra Nevada Foothills, highlighting important soil series in each region.

Soil Formation

Because California is at the confluence of several tectonic plates (see Chapter 2) it has a diverse geology giving rise to diverse parent materials (Figure 5) that result in a mosaic of soils that vary in their ability to support trees, shrubs and herbaceous vegetation. Hans Jenny (1994) described five soil-formation factors that account for differences in soils.  The characteristics and properties of soil are determined by physical, biological and chemical processes that result from the interaction of these five soil-forming factors.  The five factors (parent material, climate, topography, organisms and time) are discussed here as they relate to different annual rangeland soils.

Figure 5.  General map of the lithology of soil parent materials in the California.
Figure 5. General map of the lithology of soil parent materials in the California.

Figure 5. General map of the lithology of soil parent materials in the California.

Parent material is an important factor, particularly in the formation of upland soils. Parent material is generally defined as the unconsolidated material from which soils form. Parent material can be transported by wind, water, ice or gravity. It can also exist as bedrock that has weathered in place. Upland soils are fairly youthful in developmental stage and the parent material has a great effect on what the soil eventually looks like. Soil texture, pH and mineral constituents are soil characteristics that come from parent material. 

Climate is often considered the most powerful soil-forming factor. Climate is expressed as both temperature effects and rainfall effects. Temperature controls rates of chemical reactions. Many reactions proceed more quickly as temperature increases. Warm-region soils are therefore normally more developed or more mature than are cool-region soils. Rainfall affects leaching, pH and soil aeration. In many settings the timing of precipitation is as important as the amount. In addition to direct effects of climate, climate also profoundly affects vegetation which in turn also affects soil formation.

Topography governs soil formation by controlling the fate of water and sediment across the landscape. In general, the steeper the slope, the shallower the soil because water runs off steep slopes readily, which means that there is less moisture percolating into the soil. Moreover, high runoff causes erosion, and on steep slopes, the rate of erosion tends to outpace that of soil formation. On gentle slopes and flat areas, deeper soils can develop because there is more effective rainfall and less erosion.  The influence of aspect (the direction a slope faces) has a large effect on soil temperature, and therefore soil formation, especially in the southern and dryer parts of the Coast Range. Commonly soils are shallower on the hotter and drier south-facing aspects and deeper on the cooler north-facing aspects. In the southern and dryer parts of the Coast Range organic matter content in soils formed on south-facing aspects is usually lower than that found on north-facing aspects. 

Organisms affect and are affected by soil formation. Trees, grass, and shrubs each have different influences on soil and there is a relationship between the soil and what grows on it. Different soils form in a grassland than under a shrub or woodland vegetation.  Much of this difference is due to the rapid nutrient cycling in grasslands. Vegetation intercepts rainfall,  thereby influences runoff and therefore erosion. Vegetation type and amount directly influences the type and amount of organic matter accumulation on the soil, and thereby influences such soil chemical properties as pH and nutrient supply. Finally, vegetation is the food source for most microorganisms so the vegetation exerts a strong influence on soil microbial populations. Burrowing organisms such as pocket gophers, ground squirrels and earthworms mix the soil.

Time is the magnifier of other soil forming factors.   Soils develop and change over time. The length of time a soil has been in place has a tremendous influence on the soil profile.  For example, the Columbia Series is a recent alluvial soil, maybe a thousand years or less in age, and is uniform, sandy, pale brown and deep. In contrast, the San Joaquin Series is older, approximately 150 to 300 thousand years old, and as a result, it contains reddish brown, clay rich horizons and cemented layers that impede roots and percolating water.

The Coast Range Region

Geography

Physiographically the Coast Range is part of the Pacific Mountain System.  Most of MLRA 15 is made up of the Coast Range with the Klamath Mountains at the extreme northern end and the Los Angeles Ranges at the southwest corner of the MLRA.  The town of Clearlake is almost in the center of the northern part of this MLRA, and the towns of Suisun City and Benicia are at the south end of the northern half. The towns of Martinez and Concord are in the north end of the southern half of the area. The towns of Atascadero and Paso Robles are in the south end of the southern half. Interstate 80 crosses the junction of the northern and southern halves of the area, directly north of the Carquinez Straits, which connect the Sacramento-San Joaquin Delta with San Pablo Bay (USDA NRCS 2006).

Geology       

The Coast Range Province extends from the Transverse Ranges to the Oregon border (Figure 6) for approximately 1,000 km. From the Pacific Ocean the Range extends roughly 130 km to the Central Valley. The east-west extension of the Coast Range is considerably less in northern California where it borders the Klamath Mountains. The general topography of the Coast Range is characterized as tectonically controlled north-west trending mountains interspersed by parallel valleys. The terrain is rugged in most places with steep slopes reaching elevations as high as 2,300 m (7546 ft) in places (Harden, 2004).

Figure 6.  Coast Range Province.
Figure 6. Coast Range Province.

The Coast Range is derived from rocks of the Franciscan Assemblage, Great Valley sequence and Salinian block. The Franciscan Assemblage and Great Valley sequence consist primarily of interbedded sandstone (grey wacke) and mudstone (shale). Chert, conglomerates, schists and serpentinite are commonly encountered in this terrain, but to a lesser extent. Uplift, faulting, compression and folding of the interbedded marine deposits of the Franciscan Assemblage and the Great Valley sequence has resulted in a highly complex sequence of contrasting lithology throughout the Coast Range. The Salinian block occurs west of the San Andreas Fault line primarily in the southern half of the Coast Range. It consists mainly of granite. Volcanic rocks consisting of rhyolite, basalt, pyroclastic flows and andesite are exposed along the central coast and east of the San Andreas Fault. The age of these rocks becomes progressively younger from the south, where rocks are up to 15 million years old, to the north in the Clear Lake Volcanic fields where events are as recent as 10,000 years (Harden, 2004).

Climate

Coastal temperatures are mild, often with small differences (<6°C,< 43°F) between summer and winter mean annual soil temperatures. Warm soil temperatures are common throughout the inland areas with mean annual soil temperatures between 15-22°C (59-72°F). Cooler mean annual soil temperatures (8-15°C, 46-59°F) are found at elevations above 1,220 m (4003 ft), particularly on north-facing slopes (O’Geen et al.  2008). Mean annual precipitation ranges from 510 to 3050 mm (20-120 in) in the north to 150 to 1015 mm (6-41 in) in the southern and central Coast Ranges. These differences in climate influence soil development. Cool moist regions support Mollisols and Alfisols. Ultisols are found on stable landscapes where precipitation is highest. Entisols, Inceptisols and Aridisols are found in dry and hot regions.

Upland Soils

The Coast Range was created by transform motion and compression along the Pacific and North American Plate boundary approximately 3.5 to 5 million years ago. Thus, the Coast Range is quite young and the associated topography reflects this with steeply sloping dissected uplands separated by ephemeral stream valleys.  A common geomorphic feature, particularly in hillslopes formed from standstone and shale are spoon- shaped hollows, which are concave hillslopes mantled by thick colluvium. In this geomorphic setting, deep soil series such as Los Osos and Yorkville are commonly observed where sediment has accumulated. Landscape positions where sediment is lost by erosion and mass wasting support Soil Series such as Bonnydoon.  The initial formation of these hollows is believed to occur by landslides caused by rapid uplift and slope failure along contact zones of different rock types and along joints and fractures. Over time, these hollows fill with sediment. Periodically, during winter storm events, soils towards the base of these hollows become super saturated with water, and due to the high pore water pressures cause debris flows and soil creep (Dietrich and Dorn 1984).  The hummocky surface throughout the Franciscan terrain reflects the dynamic nature of this landscape (Figure 7).

Figure 7. Photograph of a recent landslide creating hummocky terrain in the Coast Range.
Figure 7. Photograph of a recent landslide creating hummocky terrain in the Coast Range.

Despite the complex lithology and topography of the region, soil variability is relatively low from a taxonomic standpoint. There are over 5 million hectares of land inventoried by soil survey in the region. Over 77% of this land consists of five soil great groups (Haploxerolls, Haploxeralfs, Xerorthents, Argixerolls, and Haploxererts). Great groups are a mid-level classification point in the hierarchy of Soil Taxonomy. A majority of the region supports Haploxerolls, part of the Mollisol soil order. These soils are typically referred to as grassland soils having thick topsoils, rich in soil organic carbon. Mollisols are common throughout the west side of the Coast Range where temperatures are mild relative to warmer inland soils, which may encourage soil organic matter accumulation by slowing microbial activity and decomposition of plant residues.  Mollisols are also common in parent materials derived from shale, because soils weather rapidly to smectite clays. Soil organic matter has been shown to accumulate preferentially on smectite clays (Gonzalez and Laird, 2003), thus clay mineralogy inherited from certain parent materials may partially control the distribution of Mollisols in the Coast Ranges. 

Intermediately weathered soils (Haploxeralfs) are also common in the Coast Ranges, occupying approximately 766,841 ha (1,894,905 a) in the region. These soils have thinner topsoils with less soil organic matter compared to Haploxerolls, but are more developed, displaying an illuivial clay increase in the subsoil. Haploxeralfs are common throughout the inland areas of the Coast Ranges where precipitation is moderate and temperatures are high. Weakly developed soils (Haploxerepts and Xerorthents) occupy a combined 1.5 million hectares typically occurring on steep slopes, convex landforms and steep, south-facing slopes in semi-arid regions of the Coast Range (Beaudette and O’Geen, 2008). These weakly developed soils commonly occur on granitic parent materials, Haploxerolls included. Desert soils (Torriorthents and Haplocambids) are found in the southeastern Coast Range, particularly on south-facing slopes. Ultimately weathered soils (Ultisols) characterized by low base saturation and clay-rich subsoils are found on old, stable landscape positions in the northern portion of the Coast Range where precipitation is high. Soils derived from volcanic rocks such as the Pinnacles formation include Argixerolls on gentle slopes and terraces, Haploxerolls on steep north-facing slopes and Xerorthents on steep south-facing slopes.  Valley landscape positions typically support Haploxererts, clay-rich soils with high shrink-swell capacity. These soils are also common on lower slope angles of hillslopes from parent material derived from shale.

The eastern and southeastern portions of the southern and central Coast Ranges are dominated by Moreno shale, which is an old sea floor containing selenium-rich pyrite (iron sulfide). When the minerals are exposed to oxygen, sulfides are oxidized to sulfuric acid, which creates an extremely acidic soil environment with pH values below 4.0. In more arid areas within this zone of parent material, sulfate-bearing secondary minerals such as jarosite and gypsum form. Many arid soils in this region are rich in selenium, which commonly substitutes for sulfur in the mineral precursors. Toxic levels of selenium are encountered in drainwater from these soils (Tanji et al. 1986, O’Geen et al. 2007).

The nature of upland soils throughout the Coast Range is controlled by additions, losses and translocations. Processes such as sediment transport, bioturbation, clay illuviation and organic carbon accumulation are influenced by hillslope characteristics (slope, aspect and curvature) and primary productivity. In soil landscapes derived from sandstone, hillslope positions that shed water and sediment such as convex positions and steep slopes typically support shallow soils with low soil organic carbon content and more sand and gravel relative to clay. In contrast, landscape positions that accumulate water and sediment such as concave positions, footslopes and toe slopes tend to support deep soils with thick, carbon-rich topsoils and well-mixed distributions of sand, silt and clay (Gessler et al. 2000, Beaudette and O’Geen  2008).  Well-developed soils with argillic horizons are present at lower slope angles (Argixerolls, Haploxeralfs and Palexerolls) where the rate of erosion and soil formation are at steady state. These soils are typically classified as Haploxeralfs and Argixerolls. Sheet and rill erosion by overland flow has been discovered to be negligible (Prosser and Dietrich 1995). Similar findings of limited overland flow have been reported in soils derived from shale.

Gopher (Thomomys bottae) disturbance is a dominant process in soil formation in the Coast Range. Gopher burrowing creates homogenized soils having thick, and well-mixed topsoils (Figure 8) (Yoo et al. 2005). Moreover, on steeper slopes, soil mixing by gopher activity brings subsoil material to the surface as mounds that are subsequently transported downslope (Black and Montgomery 1991). In soils derived from shale, thickening of the soil profile at down-slope positions has been attributed to shrink-swell processes, soil creep and bioturbation (McKean et al. 1993).

Figure 8.  Well mixed topsoil.
Figure 8. Well mixed topsoil.

Figure 8.  Well mixed topsoil.

Lowland Soils

Low order stream systems have aggrading valleys, typically with deeply incised stream channels, where stream power is not high enough to evacuate valley fill. Progressive headcutting of hillslopes may account for the consumption and breaching of drainage divides, termed stream piracy or stream capture. Stream capture occurs when tectonically induced elongation of a drainage system breaches a divide through headward erosion. The significance of stream piracy is evident in the complexity of lowland soils that are encountered in parts of the Coast Ranges. A sequence of different-aged valley landforms (floodplains and terraces) can be encountered because stream capture is a non-synchronous process over the evolution of a drainage system. As a result, the degree of soil development across stranded valley landforms versus more contemporary floodplains and terraces can be very different. Older soils found in stranded valleys typically have redder hues and argillic horizons.  Younger soils of the main drainage lack Bt horizons and show no evidence of reddening (Munk  1993).

High-shrink swell soils (Vertisols) are also common in lowland positions. The clay minerals that characterize these soils (smectite clays) form in landscape positions where silica and base cation concentrations are high, such as toe slope positions that receive weathering products from upslope positions. Vertisols also commonly form in low-energy depositional environments in valley alluvium.

Extensive Soil Series

Haploxerolls Soil Great Group

There are five extensive soil series in MLRA 15 at this (Hapaloxerolls) Great Group level of Soil Taxonomy:

  • Nacimiento
  • Santa Lucia
  • Linne
  • San Benito
  • Sheridan

 

Nacimiento, Santa Lucia, and Linne soils all have similar parent material in that they formed from colluvium and residuum.  They all weathered from shale and sandstone rock sources and have similar climate.  All three of these soils have soil depth that ranges from 51 cm to 1 meter deep to the underlying bedrock.  All three soils are also in a fine-loamy particle-size class.  Two of these soil series (Linne and San Benito) have a dark colored surface horizon (identified in the taxonomic class as a Pachic Epipedon) with more than 1 percent organic matter that extends to at least a depth of more than 50 cm.  Linne and San Benito soil series are further separated by the occurrence of carbonate higher in the soil profile than in the San Benito soil series.

Sheridan soils have granite parent material that separates them from Santa Lucia soils that formed in hard Monterey Shale parent material.   Both of these soil series also have a dark colored surface horizon (identified in the taxonomic class as a Pachic Epipedon) with more than 1 percent organic matter that extends to at least a depth of more than 50 cm (19.6 in).  They are however, strongly distinguished by their particle-size class with Santa Lucia soils in a clayey-skeletal particle-size class and Sheridan soils in a coarse-loamy particle-size class.  This physical distinguishing characteristic is very significant since Santa Lucia soils have much more clay and rock fragments (> 2 mm [0.08 in] in diameter) than Sheridan soils.

Haploxeralfs Soil Great Group

Vallecitos soils in MLRA 15 are a dominant soil series in the Haploxeralfs Great Soil Group.   Vallecitos soils are shallow soils that are only 25 cm to 51 cm (10-20 in) deep over hard metamorphosed sandstone and shale parent material.  They are in a clayey-skeletal particle-size class which distinguishes them from the Fallbrook soil series, another dominant soil classified in the Haploxeralfs Great Group that is in a fine-loamy particle-size class.  Fallbrook soils are moderately deep soils that are 100 to 152 cm (39-60 in) deep over granitic rock parent material.  They are also distinguished from Fallbrook soils by their location in California (Fallbrook soils occur in MLRA 20 primarily but also in MLRA 18).

Haploxerepts Soil Great Group

Millsholm soils in MLRA 15 are an extensive soil series in the Haploxerepts Soil Great Group.  Millsholm soils are shallow soils that are only 25 cm to 51 cm deep over hard shale and sandstone parent material.  They are in a fine-loamy particle-size class which has 18 to 30 percent clay content in the subsoil.

Xerorthents Soil Great Group

There are five extensive soil series in MLRA 15 at this Great Group level of soil classification that illustrate differences in soil characteristics.  Differences in soil characteristics can often be explained in the context of differences in soil formation factors.  These five dominant and extensive soils series are:

  • Cieneba
  • Gaviota
  • Shedd
  • Wisflat
  • Arburua

Cieneba soils are one of the most extensive soil series mapped in California.  Cieneba soils are mapped dominantly in MLRA 20 and MLRA 15 and to a lesser extent, in MLRA 18.  They have granitic parent material that separates them from the other four dominant soil series in the Xerorthents Great Group that formed in material weathered from sandstone or shale.  Cieneba soils are very shallow or shallow soils that are less than 51 cm deep to granitic parent material.  Clay content is less than 18 percent throughout the soil profile.  Soil depth and the prevalence of chaparral limit the grazing potential of this extensive soil.

Gaviota soils are mapped dominantly in MLRA 15 and to a lesser extent in MLRA 20.  They are shallow soils between 15 cm and 51 cm (6-20 in)deep to hard sandstone or meta-sandstone parent material.  Wisflat is a similar shallow soil mapped in the same Great Group that has sandstone and shale parent material.  Gaviota soils do not have carbonates which distinguish them from Wisflat soils that have carbonates in most of the soil profile.   Wisflat soils are another extensive soil series that are shallow soils (28 cm to 51 cm deep) over hard sandstone or shale parent material.  These soils are in a loamy particle-size class with clay content of 5 to 18 percent.

Shedd and Arburua soils are also extensive and classified in the Xerorthents Great Group.  Shedd soils are moderately deep soils between 61 cm to 100 cm (24-39 in) deep over shale parent material.   Arburua soils are also moderately deep soils between 51 cm and 100 cm (24-39 in) over sandstone and shale parent material.  Shedd soils are in the fine-silty particle-size class as opposed to fine-loamy particle-size class for Arburua soils.  Soils that are in the fine-silty particle-size class usually have a higher available water capacity than those in a fine-loamy particle-size class.

Argixerolls Soil Great Group

Los Osos soils in MLRA 15 are an extensive soil series in the Argixerolls Soil Great Group.  Los Osos soils are moderately deep soils that are 51 cm to 1 meter deep over sandstone or shale.  They have a significant increase in clay in the subsoil which averages 35 to 50 percent clay content.  Los Gatos soils are another extensive soil series in this Soil Great Group however very steep slopes and the prevalence of chaparral limit grazing potential of this soil.  Los Gatos soils are moderately deep soils that are 61 cm to 1 meter deep over hard sandstone.  They have a significant increase in clay in the subsoil which has less than 35 percent clay content.

Haploxererts Soil Great Group

Diablo and Altamont soils in MLRA 15 and to a much lesser extent, MLRA 20 are extensive soil series in the Haploxererts Soil Great Group.  These clay-rich, high shrink-swell soils are often referred to as Vertisols since they are in the Vertisols Soil Order in the Keys to Soil TaxonomyDiablo soilsare deep or very deep (1 meter to 2 meters) to shale or fine-grained sandstone parent material.  Altamont soils are deep (1 meter to 1.5 meters) to fine-grained sandstone and shale parent material.  Ayar soils in MLRA 15 are another soil series that is classified in the Haploxererts Soil Great Group.  Ayar soils are deep or very deep (1 meter to 2 meters) to shale or sandstone parent material.  Sehorn soils located primarily on the eastern slopes of the northern Coast Range, north and west of the Sacramento Valley, are an extensive soil series in the Haploxererts Soil Great Group.  Sehorn soils are moderately deep (51 cm to 1 meter) to shale and fine-grained sandstone parent material.  Climara soils are another important niche soil in the MLRA 15 Haploxererts Soil Great Group.  Climara soils are moderately deep (51 cm to 1 meter) to hard serpentine-related parent material.  Landslides and soil creep as well as high shrink-swell properties of Climara soils make fencing difficult.

The effects of mineralogy in the Vertisol Soil Order and Haploxererts Soil Great Group are expressed by large cracks in the soil when dry and closure of these same cracks when wet.  Excessive shrinking and swelling of these soils may force fence posts and even some trees out of the ground.  Vertisols in MLRA 15 are often dominated by grass vegetation with some areas of oaks, pines or junipers cropping up closer to bedrock parent material where the trees gain a foothold as the roots follow the water in cracks between the rocks.     

Palexeralfs Soil Great Group

Pinnacles soils are an example of highly weathered rangeland soils.  Pinnacles soils are moderately deep (64 cm to 1 meter) to sandstone or tuffaceous and arkosic consolidated sediments parent material.  They have a pronounced clay increase in the subsoil of 15 to 20 percent more clay (absolute) than the A horizon.   Clay content in the subsoil averages 35 to 45 percent.

The Corning series is an extensive soil in MLRA 17.  Large areas of this soil are utilized for livestock grazing.  This series formed in alluvium weathered from mixed rock sources on high terraces with mound intermound microrelief.  These reddish-colored soils have a pronounced clay increase in the subsoil.   Clay content in the upper 51 cm of the subsoil averages 35 to 55 percent.  Content of rock fragments (> 2mm in diameter) may be as high as 50 percent with 0 to 15 percent cobbles.  These characteristics make this soil difficult to farm for crops.

Positas soils in MLRA 17 are moderately extensive soils in the Palexeralfs Soil Great Group that is utilized for livestock grazing.  According to the Official Series Description, the primary use of these soils is range.  They formed in alluvium weathered from mixed rock sources on stream terraces.  These reddish-colored soils have a pronounced clay increase in the subsoil with 20 to 35 percent more total clay than the overlying A horizon that also has up to 35 percent rock fragments.  These characteristics make this soil difficult to farm for crops.

Xerofluvents Soil Great Group

Cortina soils are a moderately extensive soil in in the Xerofluvents Soil Great Group.  They occur in small valleys, alluvial fans, and floodplains in MLRA 15 and in MLRA 14 and 17.  They are formed in very deep gravelly alluvium from mixed rock sources.  They are in a loamy-skeletal particle-size class and have rock fragment content that averages 35 to 65 percent in all parts of the soil profile.  Organic matter decreases irregularly with depth which indicates the episodic nature of deposition of sediments.   The low position of Cortina soils in the landscape is ideal for capturing runoff from surrounding hills, however the high percentage of rock fragments reduces the available water capacity in the soil.  Soil in numerous small valleys within areas of hills or mountains in MLRA’s 15, 18, and 20 have potential for storage of runoff water from surrounding landscapes.  Generally landforms such as floodplains, stream terraces, and fan remnants that are associated with these valleys produce good forage for livestock grazing.  Many areas in these landforms are now utilized for crops.   

Torriorthents Soil Great Group

 Delgado soils in MLRA 15 are a good example of Aridic Moisture Regime soils in the Torriorthents Soil Great Group.  Delgado soils are shallow (18 to 51 cm) to hard sandstone or shale parent material.  Communications with local ranchers in the Kings County area indicate that some of their highest producing soils for production of forage for livestock grazing are shallow soils such as Delgado.  In these arid areas during somewhat normal rainfall patterns, all precipitation that falls is able to enter the soil with very little loss through the soil profile. 

Haplocambids Soil Great Group

Kettleman and Mercey soils in MLRA 15 are good examples of Aridic Moisture Regime soils in the Haplocambids Soil Great Group.  They are moderately deep (51 cm to 1 meter) to sandstone or shale parent material.  Mercey soils are in the fine-silty particle-size class as opposed to fine-loamy particle-size class for Kettleman soils.  Soils that are in the fine-silty particle-size class usually have a higher available water capacity than those in a fine-loamy particle-size class.

Haplargids Soil Great Group

Milham soils in the south part of the San Joaquin Valley (MLRA 17) are an extensive soil in the Haplargids Soil Great Group.  Much of this soil is farmed for crops but the lack of available irrigation water in this arid region has resulted in some areas of this soil that are still used for livestock grazing.  These soils formed in alluvium from granitic and sedimentary rock on alluvial fans, alluvial plains, low terraces, and fan remnants.  The A horizon has clay content of 5 to 20 percent and there is an increase in clay content to 20 to 35 percent in the subsoil.  Gravel content is 0 to 10 percent.

Natrargids Soil Great Group

Polvadero soils on the west side of Fresno County in the San Joaquin Valley (MLRA 17) are a moderately extensive soil in the Natrargids Soil Great Group.   Much of this soil is farmed for crops but the lack of available irrigation water in this arid region has resulted in some areas of this soil that are still used for livestock grazing.  These soils formed in alluvium from calcareous sedimentary rock on fan remnants.  The A horizon has clay content of 6 to 18 percent and there is an increase in clay content in the subsoil that has 18 to 30 percent clay content.  Gravel content is 0 to 10 percent.  The sodium adsorption ratio of the subsoil is 13 to 50.  The calcium carbonate equivalent is 5 to 30 percent in the subsoil.

The Sierra Nevada Foothill Region

Geography

Annual rangelands, including annual grasslands, oak-woodlands and chaparral generally occur along the Sierra Nevada Foothills below 900 m (3000 ft) elevation.  MLRA 18 (Figure 2) and the eastern edge of MLRA 17 (Figure 3) are within this region.  California State Highway 49 traverses the middle third of  MLRA 18, and Interstate 80 crosses the midpoint of the region. The communities of Oroville, Auburn, Folsom, Sonora, Mariposa, Coarsegold and Auberry are in this region.

Geology

The Sierra Foothill Region (MLRA 18) has a complex assemblage of many different rock types. The northern foothills consist mainly of metavolcanic and volcanic rocks (basalt, greenstone, and andesite). The central foothill region consists of a complex mixture of rock types including metasedimentary, metavolcanic, sedimentary, volcanic and igneous intrusive, which include schist, slate, phyllite, greenstone, serpentinite, chert, marble, granite and quartzite.  The southern foothill region is largely granitic with some volcanic rocks interspersed. Volcanism was common in the Sierras between 20 million and 5 million years ago.  Volcanic activity that originated east of what is now the Sierra crest extruded massive basaltic lava flows and andesitic lahars that followed ancient drainage systems all the way to the Sacramento Valley floor. The remnants of these deposits can be seen as table mountains throughout the region. This inverted topography was formed where ancient river valleys were impounded with volcanic rock and the surrounding older terrain was removed by erosion (Figure 9). To a lesser extent rhyolitic ash deposits and lahars were deposited, particularly in the northern and central Sierra.  

Figure 9.  Example of a table mountain.
Figure 9. Example of a table mountain.
  

Figure 9. Example of a table mountain.

Climate

The average annual precipitation for most of the Sierra Foothill Region ranges from 45 to 114 cm (18 to 45 in) increasing from south to north and with elevation.  Precipitation is as little as 20 cm (8 in) in the southern end of the region.  The climate is Mediterranean with cool moist winters and hot dry summers.  Mean annual air temperature ranges from 8 to 19 C (47 to 67 F).  The frost-free period is near 275 days ranging from 180 to 365 and decreases in duration from south to north and with elevation.

Upland Soils

Much of the Foothill region (MLRA 18) consists of steep slopes drained by very steep sided canyons. The granitic foothill landscapes are typically more hilly with rounded hilltops, convex and concave hillslopes and a network of small interconnected lowlands.

Soils developed from marble, serpentinite and metavolcanic rocks display the greatest degree of development in areas where water is not limiting. These soils typically have subsurface clay contents that exceed 30% and strong red colors throughout much of the profile. Soils derived from andesitic materials display the similar trends. Moreover, soils derived from greenstone often have claypans, horizons that show abrupt clay increase (>10%) over a short vertical distance (<2 cm). These horizons create seasonal perched water tables that, in sloping terrain, result in subsurface lateral flow that supplies a significant component of streamflow in ephemeral streams (Swarowsky et al., 2012).  Sierran Foothill soils derived from metasedimentary and granitic rocks tend to show less evidence of pedogenic transformations. These soils have less red coloration, which suggests lower pedogenic iron content and release of iron from primary minerals through chemical weathering. Clay contents tend to gradually increase with depth, typically to a maximum of 30%.  With the exception of soils derived from granite, most foothill soils have considerable rock fragment content with median values exceeding 20%, particularly in the subsoil.

Soil depth is perhaps the most important soil property governing the quantity of water and nutrients in semi-arid landscapes. At elevations below 450 m (1500 ft) weathering is limited by lack of precipitation, thus soil thickness is generally low. Soils derived from granite are typically moderately deep with depths between 50 and 100 cm (20 to 40 in), but increases dramatically at elevations that exceed 450 m (1500 ft), where precipitation increases. Soils derived from marble tend to be very deep. Soils derived from metavolcanic  and metasedimentary rock are often around 1-m (3.3 ft) in thickness. Soils derived from serpentinite and slate are commonly less than 1-m (3.3 ft) deep and in many instances shallow (less than 50-cm, 20 in). Moreover, soils formed from more recent basaltic lava flows are also shallow to bedrock and occupy a microtopographic sequence of mounds and swales on the flow surface, giving rise to vernal pool landscapes.

Extensive Soil Series

This section examines the 11 most extensive soils utilized for livestock grazing in MLRA 18.  They are mapped and classified in 5 Soil Great Groups.  All of them are in the Xeric Soil Moisture Regime.

Haploxeralfs Soil Great Group

Auberry soils are the most extensive soil series in MLRA 18.  Auberry soils are deep (1 meter to 1.5 meters) to weathered, intrusive, acid igneous rocks, principally quartz diorite or granodiorite parent material.   They have an increase in clay in the subsoil which averages 20 to 30 percent clay content.  

Blasingame, Ahwahnee, and Coarsegold soils are all extensive soils in MLRA 18 in the Haploxeralfs Soil Great Group.  All three soil series are moderately deep (51 cm to 1 meter) to weathered bedrock parent material.  Blasingame soils formed in material weathered from basic igneous rocks, Ahwahnee soils formed in material weathered from granitic rock.  Coarsegold soils formed in material weathered from schist.  All three soils have an increase in clay in the subsoil however Ahwahnee soils have less than 18 percent clay content in the subsoil and are in a coarse-loamy particle-size class.   Blasingame and Coarsegold soils have reddish brown color in the subsoil and are in a fine-loamy particle-size class with loam, clay loam, or sandy clay loam textures in the subsoil.

Xerorthents Soil Great Group

Cieneba soils are one of the most extensive soil series mapped in California.  Cieneba soils are mapped dominantly in MLRA 20 and MLRA 15 and to a lesser extent, in MLRA 18.  They formed in material weathered from granitic parent material.  Cieneba soils are very shallow or shallow soils that are less than 51 cm deep to weathered granitic parent material.  Clay content is less than 18 percent throughout the soil profile.  Soil depth and the prevalence of chaparral limit the grazing potential of this extensive soil.

Haploxerepts Soil Great Group

Auburn soils in MLRA 18 are extensive soils that are shallow to moderately deep (25 cm to 71 cm) to material weathered from metabasic or metasedimentary rock such as amphibolite schist, greenstone schist, or diabase parent material.  Auburn soils have textures of loam, silt loam, or clay loam or gravelly, stony, or very stony equivalents.

Toomes soils in are extensive soils in MLRA 18 on plateaus and ridges of volcanic flows and on foothills of volcanic uplands.  They are very shallow or shallow (10 cm to 51 cm) and formed in material weathered from tuff breccia, basalt, and andesite parent material.  Toomes soils have textures of loam, silt loam, or clay loam.  Pebble, cobble, and stone content is 10 to 35 percent.

Vista soils are extensive soils that occur in MLRA 18 and also in MLRA 20 and MLRA 15.  They are moderately deep (51 cm to 1 meter) soils that formed in material weathered from decomposed granitic rock parent material.  Textures are coarse sandy loam, sandy loam, or loamy sand.

Argixerolls Soil Great Group

Arujo soils are moderately extensive soils in MLRA 18 in the Argixerolls Soil Great Group that are deep (1 meter to 1.5 meters) soils formed in material weathered from metamorphic and igneous (primarily granitic) rock parent material.  Organic matter content is more than 1.2 percent to a depth of 51 cm or more.  The subsoil has loam, clay loam, or sandy clay loam texture that has about 5 to 11 percent more clay content (absolute) than the A horizon.

Haploxerolls Soil Great Group

Pentz soils are extensive soils in MLRA 18 in the Haploxerolls Soil Great Group.  They are shallow (25 cm to 51 cm) soils formed in material weathered from weakly consolidated basic andesitic tuffaceous sediments parent material.  Organic matter content in the upper 18 cm is 1 to 3 percent. They have fine sandy loam, sandy loam, or loam texture with clay percent of 8 to 20 percent with gravelly or cobbly equivalents.

Walong soils are extensive soils in MLRA 18 in the Haploxerolls Soil Great Group.  They are moderately deep (51 cm to 1 meter) soils formed in material weathered from granitic rock parent material.  Organic matter content is more than 1 percent to a depth of 36 cm to 46 cm.  They have sandy loam, gravelly sandy loam, or coarse sandy loam textures. 

Summary

Soil formation results from the action of climate and organisms upon parent material.  Because of California’s complex geology the number of distinct soils is great and their arrangement complex.  The type of soil available on rangeland is important not only for the limits it places on vegetation but also for other ecosystem services such as clean water. 

Soil is the medium that supports rangeland vegetation and moderates the effects and fate of precipitation.  While rainfall varies with longitude and elevation, it influences vegetation structure (trees, shrubs and herbaceous layers), species composition and productivity.  Soil depth, texture and water holding capacity strongly influence the length of the growing season when adequate soil moisture is available.  Influencing plant productivity and water quality, nutrient cycling is strongly influenced by parent material and organisms (vegetation and soil biota).

Soil also limits the type of management that can be applied to a particular site.  By classifying soils and land types rangeland managers are able to develop management objectives that are within the capabilities of the land being managed.   Recognizing soil and site differences during conservation planning encourages selection of practices that can effectively support management objectives.  Thus it is crucial that scientists and managers continue to learn about soils and improve the management of the soil component of ecological sites.

 

Soils on the Web (Sidebar)

Soil Web 

(http://casoilresource.lawr.ucdavis.edu/soilweb/)

SoilWeb was developed by the California Soil Resources Lab in the Department of Land, Air and Water Resources at the University of California, Davis.  Using mobile and PC interfaces the user can explore mapped soil survey areas using interactive Google Maps or Google Earth.  They can view detailed information about map units and their components.

USDA NRCS Soils Website

(http://www.nrcs.usda.gov/wps/portal/nrcs/site/soils/home/)

This website provides access to Web Soil Survey, Official Soil Series Descriptions, Soil Data Access, Soil Data Viewer, Soil Lab Data, Technical Resources, and Published Soil Surveys.

 

Literature Cited

Beaudette, D., and A.T. O’Geen.  2008. Quantifying the aspect effect: An application of solar radiation modeling for soil survey. Soil Science Society of America Journal. 73:1345-1352.

Black, T. A., and D. R. Montgomery. 1991. Sediment transport by burrowing mammals, Marin County, California.  Earth Surface Processes and Landforms 16:163–172.

Dietrich, W.E. and R. Dorn. 1984. Significance of thick deposits of colluvium on hillslopes: A case study involving the use of pollen analysis in the coastal mountains of northern California. Journal of Geology 92:147-158.

Gessler, P.E., O.A. Chadwick, F. Chamran, L. Althouse and K. Holmes. 2000. Modeling soil-landscape and ecosystem properties using terrain attributes. Soil Science Society of America Journal 64:2046-2056.

Gonzalez and Laird. 2003. Carbon sequestration in clay mineral fractions from 14C-labeled plant residues. Soil Science Society of America Journal 67:1715-1720.

Jenny, H. 1941. Factors of Soil Formation. New York, NY: McGraw-Hill Book Company. 281 pgs.

McKean, J. A., W. E. Dietrich, R. C. Finkel, J. R. Southon, and M. W. Caffee. 1993. Quantification of soil production and downslope creep rates from cosmogenic 10Be accumulations on a hillslope profile. Geology 21:343-346.

Munk, L.P. 1993. Stratigraphy, geomorphology, soils and neotectonic interpretation of the Dunnigan Hills, California. Ph.D. dissertation University of California, Davis, CA.

Norton, J.B., L.J. Jungst, .L.J., U. Norton, H.R Olsen, K.W. Tate, W.R. Horwath.  2011. Soil carbon and nitrogen storage in upper montane riparian meadows. Ecosystems 14:1217-1231.

O’Geen, A.T., R.A. Dahlgren, and D. Sanchez-Mata. 2008. California Soils and Examples of Ultramafic Vegetation. M.G. Barbour, T. Keller-Wolf and A.A. Schoenherr (Eds), In: Terrestrial Vegetation of California, 3rd edition.  London, England: University of California Press.

Prosser, I. P., and W. E. Dietrich.  1995. Field experiments on erosion by overland flow and their implication for a digital terrain model of channel initiation. Water Resources Research, 31: 2867– 2876.

Swarowsky, A., R.A. Dahlgren, and A.T. O’Geen. 2012. Linking subsurface lateral flowpath activity with stream flow characteristics in a semiarid headwater catchment. Soil Science Society of America Journal 76:532-547.

Tanji, K., A. Lauchli, and J. Meyer. 1986. Selenium in the San Joaquin Valley. Environment 28:6-39.

United States Department of Agriculture, Natural Resources Conservation Service. 2006. Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin.Washington, D.C.:  U.S. Department of Agriculture Handbook 296.  669 pgs. (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/home/?cid=nrcs142p2_053624, accessed 12/16/2013).

Yoo, K. and R. Amundson. 2005. Erosion of upland hillslope soil organic carbon: Coupling field measurements with a sediment transport model. Global Biogeochemical Cycles 19: doi:10.1029/2004GB002271

 

List of Tables

Table 1. List of annual rangeland soil series.

 

List of Figures

Figure 1.  California soil lithology (http://casoilresource.lawr.ucdavis.edu/drupal/node/776).

Figure 2.  Major Land Resource Area 15 (Coast Range).

Figure 3.  Major Land Resource Area 18 (Sierra Nevada Foothills).

Figure 4.  Major Land Resource Area 17 (Sacramento and San Joaquin Valleys).

Figure 5.  Major Land Resource Area 19 (Southern California Mountains).Figure 6.  Coast Range Province.

Figure 7. Photograph of a recent landslide creating hummocky terrain in the Coast Range.

Figure 8.  Example of a table mountain.

 

Table 1.  Soil series of the annual rangelands. Some soil series are classified slightly different in different soil surveys.  This occurs because different versions of Soil Taxonomy were used during the making of different soil surveys.  Generally the older the soil survey the more changes that have occurred to Soil Taxonomy  since the soil survey was published.  These classification differences are gradually being brought up to date as soil surveys and their classifications are being updated through the soil correlation process.

Series

Subgroup

Family

Vegetation Type

Ahwahnee

Mollic Haploxeralfs

coarse-loamy, mixed, thermic

OW

Alo

Aridic Haploxererts

Fine, smectitic, thermic

AG

Altamont

Aridic Haploxererts

Fine, smectitic, thermic

AG

Amador

Typic Haploxerepts

 Loamy, mixed, superactive, thermic, shallow

 

Anaverde

Pachic Haploxerolls

Fine-loamy, mixed, active, mesic

OW/AG

Andregg

Ultic Haploxerolls

Coarse-loamy, mixed, superactive, thermic

AG/OW

Anita

Xeric Duraquerts

clayey, smectitic, thermic

AG

Antioch

Typic Natrixeralfs

Fine, smectitic, thermic

AG

Apollo

Calcic Haploxerolls

Fine-loamy, mixed, superactive, thermic

AG

Arbuckle

Typic Haploxeralfs

Fine-loamy, mixed, superactive, thermic

AG/OW

Arburua

Typic Xerorthents

Fine-loamy, mixed, superactive, calcareous, thermic

AG

Argonaut

Mollie Haploxeralfs

fine, mixed, thermic

OW

Arnold

Typic Xeropsamments

Mixed, thermic

CH/OW

Arujo

Pachic Argixerolls

Fine-loamy, mixed, superactive, thermic

OW

Asolt

 Chromic Haploxererts

Fine, smectitic, thermic

AG

Auberry

Ultic Haploxeralfs

fine-loamy mixed thermic

OW

Auburn

Lithic Haploxerepts

Loamy, mixed, superactive, thermic

OW

Ayar

Typic Haploxererts

Fine, smectitic, thermic

AG

Azule

Mollic Haploxeralfs

Fine, smectitic, thermic

AG

Balcom

Typic Calcixerepts

Fine-loamy, mixed, superactive, thermic

AG

Beam

Xeric Haplocambids

 Loamy, mixed, superactive, thermic, shallow

AG

Bearwallow

 Ultic Haploxeralfs

Fine-loamy, mixed, superactive, thermic

AG

Bellota

Abruptic Durixeralfs

Fine-loamy, mixed, superactive, thermic

AG

Bellyspring

Mollic Haploxeralfs

Fine-loamy, mixed, superactive, thermic

AG

Blasingame

Typic Haploxeralfs

 Fine-loamy, mixed, superactive, thermic

AG/OW

Boar

Mollic Haploxeralfs

Fine, smectitic, thermic

AG/OW

Botella

Pachic Argixerolls

Fine-loamy, mixed, superactive, thermic

AG/OW

Bressa

Typic Haploxeralfs

Fine-loamy, mixed, active, thermic

AG/OW

Briones

Typic Xeropsamments

Mixed, thermic

AG/OW

Buttes

Mollic Haploxeralfs

Loamy-skeletal, mixed, superactive, thermic

AG/OW

Calla

Typic Calcixerepts

Fine-loamy, mixed, superactive, thermic

AG

Calodo

Calcic Haploxerolls

 Loamy, mixed, superactive, thermic, shallow

OW

Camatta

Xeric Petrocalcids

Loamy, mixed, superactive, thermic, shallow

AG

Capay

Typic Haploxererts

Fine, smectitic, thermic

AG

Capitan

Entic Haploxerolls

Loamy-skeletal, mixed, superactive, thermic, shallow

AG

Carbona

Vertic Haploxerolls

Fine, smectitic, thermic

AG

Chamise

Ultic Palexerolls

Clayey-skeletal, mixed, active, thermic

AG/OW/CH

Chanac

Calcic Haploxerepts

Fine-loamy, mixed, superactive, thermic

 

Choice

Typic Xerorthents

Fine, mixed, superactive, calcareous, thermic

AG

Chualar

Mollic Haploxeralfs

fine-loamy, mixed, thermic

AG

Cibo

Aridic Haploxererts

Fine, smectitic, thermic

AG

Cibo

Aridic Haploxererts

Fine, smectitic, thermic

 

Cieneba

Typic Xerorthents 

Loamy, mixed, superactive, nonacid, thermic, shallow

CH

Clear Lake

Xeric Endoaquerts

Fine, smectitic, thermic

AG

Climara

Aridic Haploxererts

Fine, magnesic, thermic

AG

Coarsegold

Mollic Haploxeralfs

Fine-loamy, mixed, superactive, thermic

OW/CH

Cochora

Typic Torriorthents

Loamy, mixed, superactive, calcareous, thermic, shallow

AG

Concepcion

Xeric Argialbolls

Fine, smectitic, thermic

AG

Contra Costa

Mollic Haploxeralfs

Fine, mixed, superactive, thermic

OW/AG/CH

Corning

Typic Palexeralfs

fine, mixed, thermic

AG

Corning

Typic Palexeralfs

Fine, mixed, active, thermic

AG

Cropley

Aridic Haploxererts

Fine, smectitic, thermic

AG

Crow Hill

Pachic Haploxerolls

Fine-silty, mixed, superactive, thermic

AG

Currymountain

Typic Argixerolls

Fine-loamy, mixed, superactive, mesic

OW

Cyvar

Typic Durixeralfs

Loamy, mixed, superactive, thermic, shallow

AG

Daulton

Lithic Xerorthents

Loamy, mixed, superactive, nonacid, thermic

AG/OW

Diablo

Aridic Haploxererts 

Fine, smectitic, thermic

AG

Diamond Springs

U ltic Haploxeralfs

fine-loamy, mixed, mesic

OW/FOR

Dibble

Typic Haploxeralfs

Fine, smectitic, thermic

AG/OW

Doemill

Lithic Haploxeralfs

Loamy, mixed, superactive, thermic

 

Exclose

Calcic Haploxerepts

Fine-loamy, mixed, superactive, thermic

AG

Fagan

Typic Argixerolls

Fine, smectitic, thermic

AG/OW

Fallbrook

Typic Haploxeralfs

Fine-loamy, mixed, superactive, thermic

CH/AG

Feliz

Cumulic Haploxerolls

Fine-loamy, mixed, superactive, thermic

AG

Fifield

Ultic Argixerolls

Loamy-skeletal, mixed, superactive, thermic

OW

Fontana

Calcic Haploxerolls

Fine-loamy, mixed, superactive, thermic

AG

Fouts

Ultic Argixerolls

Clayey-skeletal, mixed, superactive, thermic

AG

Franciscan

Typic Argixerolls

Fine-loamy, mixed, superactive, thermic

OW

Friant

Lithic Haploxerolls

Loamy, mixed, superactive, thermic

CH/AG

Garey

Lamellic Haploxeralfs

Coarse-loamy, mixed, superactive, thermic

AG

Gaviota

Lithic Xerorthents

Loamy, mixed, superactive, nonacid, thermic

CH

Gazos

Pachic Haploxerolls

Fine-loamy, mixed, superactive, thermic

AG/OW/CH

Gilroy

Typic Argixerolls

Fine-loamy, mixed, active, thermic

AG/OW/CH

Gloria

Abruptic Durixeralfs

Fine, illitic, thermic

AG

Godde

Lithic Haploxerolls

Loamy, mixed, superactive, mesic

CH/AG

Goldeagle

Typic Haploxeralfs

Fine, mixed, superactive, thermic

AG/OW/CH

Gonzaga

Typic Palexerolls

Fine, mixed, superactive, thermic

OW/AG

Guenoc

Typic Rhodoxeralfs

Fine, kaolinitic, thermic

AG/OW/CH

Haire

Typic Haploxerults

Fine, mixed, superactive, thermic

AG

Hambright

Lithic Haploxerolls

Loamy-skeletal, mixed, superactive, thermic

OW/AG

Havala

 Pachic Argixerolls

Fine-loamy, mixed, superactive, thermic

AG/OW

Henneke

Lithic Argixerolls

Clayey-skeletal, serpentinitic, thermic

 

Hillbrick

Lithic Xerorthents

Loamy, mixed, superactive, calcareous, thermic

JU/AG

Hillgate

Typic Palexeralfs

Fine, smectitic, thermic

AG

Honker

Mollic Palexeralfs

Fine, mixed, superactive, thermic

AG

Hopland

Typic Haploxeralfs 

Fine-loamy, mixed, active, mesic

OW

Hytop

Typic Palexeralfs

Fine, mixed, superactive, thermic

AG

Inks

Lithic Argixerolls

Loamy-skeletal, mixed, superactive, thermic

OW

Jokerst

Lithic Haploxeralfs

Loamy, mixed, superactive, thermic

OW

Keyes

Abruptic Durixeralfs

Clayey, mixed, active, thermic, shallow

AG

Kilmer

Typic Xerorthents

Fine-loamy, mixed, superactive, calcareous, thermic

AG

Kimball

Mollic Palexeralfs

Fine, montmorillonitic, thermic

AG

Kimberlina

Typic Torriorthents

Coarse-loamy, mixed, superactive, calcareous, thermic

AG

Las Posas

Typic Rhodoxeralfs

Fine, mixed, thermic

AG/CH

Laughlin

Ultic Haploxerolls

Fine-loamy, mixed, superactive, mesic

OW

Laveaga

Typic Argixerolls

Fine, mixed, active, mesic

OW

Leesville

Pachic Haploxerolls

Fine-loamy over sandy or sandy-skeletal, magnesic, thermic

AG

Linne

Calcic Pachic Haploxerolls

Fine-loamy, mixed, superactive, thermic

AG/OW/CS

Livermore

Typic Haploxerolls

Loamy-skeletal, mixed, superactive, thermic

AG/OW

Lockwood

Pachic Argixerolls

Fine-loamy, mixed, superactive, thermic

AG/OW/CH

Lodo

Lithic Haploxerolls

Loamy, mixed, superactive, thermic

OW/CH

Lopez

Lithic Ultic Haploxerolls

Loamy-skeletal, mixed, superactive, thermic 

AG/OW/CS

Los Gatos

Typic Argixerolls

Fine-loamy, mixed, active, mesic

CH

Los Osos

Typic Argixerolls

Fine, smectitic, thermic

AG

Maxwell

Typic Haploxererts

Fine, smectitic, thermic

AG

Maymen

Typic Dystroxerepts

Loamy, mixed, active, mesic, shallow

CH

Mcmullin

Lithic Ultic Haploxerolls

Loamy, mixed, superactive, mesic

OW

Mendi

Typic Xerorthents

Fine-loamy, mixed, superactive, calcareous, thermic

AG

Millsholm

Lithic Haploxerepts

Loamy, mixed, superactive, thermic

OW

Milpitas

Mollic Palexeralfs

Fine, smectitic, thermic

AG/OW/CS

Mokelumne

Typic Haploxerults

Fine, kaolinitic, thermic

OW/CH

Montara

Lithic Haploxerolls

Loamy, magnesic, thermic

AG

Muranch

Aridic Haploxerolls

Loamy-skeletal, mixed, superactive, thermic

AG

Myers

Aridic Haploxererts

Fine, smectitic, thermic

AG

Nacimiento

Calcic Haploxerolls

Fine-loamy, mixed, superactive, thermic

AG

Newville

Mollic Palexeralfs

Fine, smectitic, thermic

AG/OW/CS

Nodhill

Typic Haploxeralfs

Fine-loamy, mixed, superactive, thermic

AG

Oneil

Calcic Haploxerolls

Fine-silty, mixed, superactive, thermic

AG

Orognen

Typic Palexeralfs

Fine, mixed, superactive, thermic

AG

Padres

Typic Calcixerepts

Coarse-loamy, mixed, superactive, thermic

AG

Panoza

Calcic Haploxerepts

Coarse-loamy, mixed, superactive, thermic

AG

Parkfield

Vertic Argixerolls

Fine, smectitic, thermic

OW/AG

Pentz

Ultic Haploxerolls

Loamy, mixed, superactive, thermic, shallow

AG

Perkins

Mollic Haploxeralfs

Fine-loamy, mixed, superactive, thermic

AG/OW

Peters

Typic Haploxeroll

Clayey, smectitic, thermic, shallow

AG

Pinnacles

Ultic Palexeralfs

Fine, smectitic, thermic

AG/CH

Placentia

Typic Natrixeralfs

Fine, smectitic, thermic

AG

Polonio

Calcic Haploxerepts

Fine-loamy, mixed, superactive, thermic

AG

Positas

Mollic Palexeralfs

Fine, smectitic, thermic

AG/OW

Pyxo

Typic Haplocambids

Coarse-loamy, mixed, superactive, thermic

AG

Quiensabe

Typic Argixerolls

Fine, mixed, superactive, thermic

OW/CH

Rackerby

Ultic Palexeralfs

Fine, kaolonitic, mesic

OW/CH

Ramona

Typic Haploxeralfs

Fine-loamy, mixed, thermic

CH

Redding

Abruptic Durixeralfs

Fine, mixed, thermic

AG

Redvine

Ultic Palexeralfs

Fine, mixed, semiactive, thermic

OW

Reliz

Lithic Xerorthents

Loamy-skeletal, mixed, active, nonacid, thermic

AG/OW

Rescue

Mollic Haploxeralfs

Fine-loamy, mixed, thermic

AG/CH

Rincon

Mollic Haploxeralfs

Fine, smectitic, thermic

AG

Ryer

Mollic Haploxeralfs

Fine, montmorillonitic, thermic

AG

Sagaser

Typic Argixerolls

Fine-loamy, mixed, superactive, mesic

OW

Saltos

Lithic Mollic Haploxeralfs

Loamy, mixed, superactive, thermic

CH/AG

San Andreas

Typic Haploxerolls

Coarse-loamy, mixed, superactive, thermic

AG

San Benito

Calcic Pachic Haploxerolls

Fine-loamy, mixed, superactive, thermic

OW/AG

San Timoteo

Typic Xerorthents

Coarse-loamy, mixed, superactive, calcareous, thermic

CA/AG

Santa Lucia

Pachic Ultic Haploxerolls

Clayey-skeletal, mixed, superactive, thermic

CS/OW/AG

Santa Ynez

Ultic Palexerolls

Fine, smectitic, thermic

OW

Saucito

Lithic Haploxeralfs

Loamy-skeletal, mixed, superactive, thermic

AG

Seaback

Calcic Haploxerepts

Loamy, mixed, superactive, thermic, shallow

AG

Sehorn

Aridic Haploxererts

Fine, smectitic, thermic

OW/AG

Semper

Gypsic Haploxerepts

Coarse-loamy, mixed, superactive, thermic

AG

Sesame

Typic Haploxeralfs

Fine-loamy, mixed, superactive, thermic

AG/OW

Shedd

Typic Xerorthents

Fine-silty, mixed, superactive, calcareous, thermic

AG

Shenandoah

Aquic Palexeralfs

Fine, smectitic, thermic

AG/OW

Sheridan

Pachic Haploxerolls

Coarse-loamy, mixed, superactive, thermic

AG/OW

Sierra

Ultic Haploxeralfs

Fine-loamy, mixed, thermic

OW

Skyhigh

Mollic Haploxeralfs

Fine, smectitic, thermic

OW

Sleeper

Mollic Haploxeralfs

Fine, smectitic, thermic

OW

Sobrante

Mollic Haploxeralfs

Fine-loamy, mixed, thermic

OW

Squawrock

Typic Haploxeralfs

Loamy-skeletal, mixed, superactive, thermic

AG/OW

Still

Cumulic Haploxerolls

Fine-loamy, mixed, superactive, thermic

AG/OW

Stonyford

Lithic Mollic Haploxeralfs

Loamy, mixed, superactive, thermic

CH

Suther

Aquic Haploxeralfs

Fine, smectitic, mesic

AG/OW/CH

Sween

Typic Argixerolls

Fine, smectitic, thermic

AG/OW

Tajea

Typic Argixerolls

Fine-loamy, mixed, superactive, thermic

OW

Talmage

Fluventic Haploxerolls

Loamy-skeletal, mixed, superactive, thermic

AG/SH/OW

Tierra

Mollic Palexeralfs

Fine, smectitic, thermic

AG

Timbuctoo

Typic Rhodoxeralfs

Fine, parasesquic, thermic

OW

Todos

Typic Argixerolls

Fine, smectitic, thermic

AG/CH/OW

Toomes

Lithic Haploxerepts

Loamy, mixed, superactive, thermic

OW/AG

Trabuco

Mollic Haploxeralfs

Fine, mixed, superactive, thermic

OW/AG

Tunis

Typic Haploxerolls

Loamy, mixed, superactive, thermic, shallow

AG

Tuscan

Typic Durixeralfs

Clayey, smectitic, thermic, shallow

AG

Vallecitos

Lithic Ruptic-Inceptic Haploxeralfs

Clayey, smectitic, thermic

AG/OW/CH

Vaquero

Aridic Haploxererts

Fine, smectitic, thermic

AG

Vernado

Pachic Haploxerolls

Coarse-loamy, mixed, superactive, mesic

OW/AG

Vista

Typic Haploxerepts

Coarse-loamy, mixed, superactive, thermic

AG/CH

Wadesprings

Pachic Argixerolls

Fine-loamy, magnesic, thermic

OW/AG

Walong

Typic Haploxerolls

Coarse-loamy, mixed, superactive, thermic

OW/AG

Wisflat

Lithic Xerorthents

Loamy, mixed, superactive, calcareous, thermic

AG

Wisheylu

Ultic Haploxeralfs

Fine-loamy, kaolinitic, thermic

OW

Witherell

Typic Haploxerepts 

Fragmental, mixed, thermic

AG

Wyman

Mollic Haploxeralfs

Fine-loamy, mixed, thermic

AG

Yokohl

Abruptic Durixeralfs

Fine, montmorillonitic, thermic

AG

Yorktree

Ultic Argixerolls

Fine, mixed, superactive, mesic

OW

Yorkville

Typic Argixerolls

Fine, mixed, superactive, thermic

AG

Zaca

Vertic Haploxerolls 

Fine, smectitic, thermic

AG

 AG=annual grassland, OW=oak-woodland, CH= chaparral, CS=coastal sage, CA=California sagebrush, BR=brush.

Webmaster Email: lmroche@ucdavis.edu