LOCATION SENTINEL CAEstablished Series
TAXONOMIC CLASS: Coarse-loamy, isotic, mesic Vitrandic Dystroxerepts
TYPICAL PEDON: Sentinel loam on a 0.5 percent slope under a mature stand of ponderosa pine, incense cedar, and black oak at an elevation of 3,970 feet (1,210.1 meters). (Colors are for dry soil unless otherwise stated. When described September 26, 1990, the soil was dry throughout.)
Oi--0 to 1 inch (0 to 3 centimeters); decomposing litter layer. (0 to 2 inches [0 to 5 centimeters] thick)
A1--1 to 5 inches (3 to 13 centimeters) grayish brown (2.5Y 5/2) loam; dark brown (10YR 3/3) moist; strong fine granular structure; slightly hard, very friable, non-sticky, slightly plastic; moderately smeary; slightly acid (pH 6.5); clear smooth boundary. (4 to 6 inches [10 to 15 centimeters] thick)
A2--5 to 20 inches (13 to 51 centimeters) brown (10YR 5/3) loam; very dark grayish brown (10YR 3/2) moist; moderate fine granular structure; slightly hard, very friable, non-sticky, slightly plastic; moderately smeary; moderately acid (pH 5.8); clear smooth boundary. (13 to 17 inches [33 to 43 centimeters] thick)
A3--20 to 27 inches (51 to 69 centimeters) brown (10YR 5/3) loam; dark brown (10YR 3/3) moist; weak medium subangular blocky structure; slightly hard, very friable, non-sticky, slightly plastic; moderately smeary; moderately acid (pH 5.9); clear smooth boundary. (5 to 9 inches [13 to 23 centimeters] thick)
Bw--27 to 41 inches (69 to 105 centimeters) light yellowish brown (10YR 6/4) loam; dark brown (10YR 3/3) moist; weak coarse subangular blocky structure; slightly hard, very friable, slightly sticky, slightly plastic; moderately smeary; few very fine sand or silt coatings on ped surfaces; moderately acid (pH 5.9); clear smooth boundary. (5 to 25 inches [13 to 64 centimeters] thick)
C1--41 to 56 inches (105 to 143 centimeters) light yellowish brown (2.5Y 6/4) sandy loam; olive brown (2.5Y 4/4) moist; massive; slightly hard, very friable, non-sticky, slightly plastic; moderately smeary; slightly acid (pH 6.2); clear smooth boundary. (10 to 20 inches [25 to 51 centimeters] thick)
C2--56 to 66 inches (143 to 168 centimeters) pale yellow (2.5Y 7/4) loamy sand; olive brown (2.5Y 4/4) moist; single grain; loose, non-sticky, non-plastic; slightly acid (pH 6.2).
TYPE LOCATION: Mariposa County, California; Yosemite Valley, about 200 yards (182.9 meters) northeast of the intersection of Southside Drive and the road north to El Capitan Bridge; Latitude 37 degrees 43 minutes 18 seconds north and Longitude 119 degrees 37 minutes 40 west; UTM Zone 11, easting 268392.21 and northing 4178194.56; USGS El Capitan, California Quadrangle, NAD 83.
RANGE IN CHARACTERISTICS: Thickness of the solum is 25 to 45 inches (63 to 114 centimeters). The mean annual soil temperature is 52 to 56 degrees F (11.1 to 13.3 degrees C). The soil temperature exceeds 41 degrees F (5.0 degrees C) from March through November and exceeds 47 degrees F (8.3 degrees C) from mid April through October. The difference between mean winter and mean summer soil temperature is about 28 degrees F (17 degrees C). The soil moisture control section is dry in all parts from early July to early November (140-160 days) and is moist in all parts from December to mid May. Fine gravel content is 0 to 5 percent. Base saturation by ammonium acetate is 50 to 70 percent in the upper part of the A horizon and decreases to 40 to 50 percent in the lower part of the A horizon. Base saturation is 35 to 45 percent in the Bw and C horizons. The sand fraction contains 5 to 20 percent volcanic glass and has other vitrandic properties. Reaction by sodium fluoride is 9.3 to 10.5.
A Horizon
Hue: 10YR or 2.5Y (dry and moist)
Value: 8 (dry) and 3 (moist)
Chroma: 2 to 6 (dry and moist)
Texture: sandy loam, fine sandy loam, or loam
Clay content: 3 to 12 percent
Organic matter content: 1 to 8 percent
Reaction: moderately acid or slightly acid
Bw Horizon
Hue: 10YR or 2.5Y (dry and moist)
Value: 6 (dry) and 3 or 4 (moist)
Chroma: 3 or 4 (dry or moist)
Texture: sandy loam, fine sandy loam, or loam
Clay content: 3 to 10 percent
Organic matter content: 0.5 to 2 percent
Reaction: moderately acid or slightly acid
C Horizon
Hue: 2.5Y (dry and moist)
Value: 6 or 7 (dry) and 4 (moist)
Chroma: 4 (dry and moist)
Texture: loamy sand or sandy loam
Clay content: 3 to 10 percent
Organic matter content: 0 to 1.5 percent
Reaction: moderately acid or slightly acid
COMPETING SERIES: These are Elcapitan and Leidig soils. Elcapitan soils are on intermediate floodplains, are somewhat poorly drained and have well defined stratification. Leidig soils are on high floodplains and are somewhat poorly drained.
GEOGRAPHIC SETTING: Sentinel soils are on lake terraces and mountain valleys. Slopes are 0 to 2 percent and are linear to slightly convex in shape. These soils formed in glaciolacustrine sediments derived from granitoid rock and some volcanic ash. Elevation is 3,955 to 3,996 feet (1,205.4 to 1,217.9 meters). The climate is subhumid with warm dry summers and cool moist winters. Mean annual precipitation is 35 to 40 inches (889 to 1,016 millimeters), some of which falls as snow. The mean annual temperature is 50 to 55 F (10.0 to 12.8 degrees C). The mean January temperature is about 36 degrees F (2.2 degrees C). The mean July temperature is about 72 degrees F. (22.2 degrees C). Frost-free period is 100 to 150 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Elcapitan and Leidig soils. Also Happyisles soils which are on slightly higher geomorphic positions, have slope of 0 to 9 percent and are on alluvial fans, fan aprons, flood plains, terraces, mountain valleys and drainageways.
DRAINAGE AND PERMEABILITY: Well drained; very low runoff; hydraulic conductivity is high or very high. Flooding is rare.
USE AND VEGETATION: This soil is used for recreation and wildlife habitat. The vegetation is Ponderosa pine, incense cedar, black oak, Douglas-fir, and sugar pine with some annual grasses and forbs in the understory.
DISTRIBUTION AND EXTENT: Glaciated mountain valleys on the west side of the Sierra Nevada Range, California. The soils are not extensive. MLRA is 22A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Yosemite Valley Part, California 2007. Proposed in 1991. Source of name is Sentinel Rock.
REMARKS: Changed from coarse-loamy, mixed, mesic Vitrandic Xerumbrepts to coarse-loamy, isotic, mesic Vitrandic Dystroxerepts because of changes in Soil Taxonomy. All lab data from the Yosemite Valley Part Soil Survey indicates isotic mineralogy. Sentinel soils have an umbric epipedon and cambic horizon. The sand fraction contains 5 to 20 percent volcanic glass and has other vitrandic properties. Reaction by sodium fluoride is 9.3 to 10.5.
Additional data: NSSL reference lab sample pedon ID S90CA-043-010 (lab data pedon samples 91P2321-91P2322) available for the A2 and Bw horizons for the typical pedon.