LOCATION LAPOSA AZEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, hyperthermic Typic Haplocambids
TYPICAL PEDON: Laposa extremely gravelly loam - desert. (Colors are for dry soil unless otherwise noted.) 70 to 80 percent of surface covered with gravel, cobble and stones.
A--0 to 3 inches; yellowish brown (10YR 5/4) extremely gravelly loam, dark yellowish brown (10YR 4/4) moist); weak thin platy structure; soft, very friable, slightly sticky; many very fine roots; many very fine tubular pores; 90 percent gravel; strongly effervescent; moderately alkaline (pH 8.2) abrupt smooth boundary. (1 to 3 inches thick)
Bw1--3 to 10 inches; light yellowish brown (10YR 6/4) extremely gravelly loam, dark yellowish brown (10YR 4/4) moist; weak fine subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many very fine roots; few very fine tubular pores; 70 percent gravel; strongly effervescent; moderately alkaline (pH 8.0); abrupt wavy boundary. (5 to 12 inches thick)
Bw2--10 to 21 inches; light yellowish brown (10YR 6/4) extremely gravelly loam, dark yellowish brown (10YR 4/4) moist; weak medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many very fine roots; many very fine irregular pores; 70 percent gravel; violently effervescent; moderately alkaline (pH 8.2); clear wavy boundary. (5 to 12 inches thick)
Bk--21 to 32 inches; light yellowish brown (10YR 6/4) extremely gravelly loam, dark yellowish brown (10YR 4/4) moist; massive; soft, very friable, slightly sticky; few very fine roots; many fine irregular pores; 80 percent coarse granite gravel calcium carbonate coated on undersides; violently effervescent; moderately alkaline (pH 8.2); abrupt wavy boundary. (5 to 13 inches thick)
2R--32 inches; hard granite.
TYPE LOCATION: Yuma County, Arizona; about 15 miles north of Imperial Dam; 1,000 feet west and 1,750 feet south of the northeast corner of section 18, T. 4 S., R. 22 W.
RANGE IN CHARACTERISTICS:
Soil moisture: Intermittently moist in some part of the soil moisture control section during July - September and December - February. Driest during May and June. Typic aridic soil moisture regime.
Rock fragments: 35 to 90 percent gravel in the control section; 15 to 85 percent in the surface layer.
Depth to base of cambic horizon: 10 to 30 inches
Depth to bedrock: 20 to 40 inches
A horizon
Hue: 10YR, 7.5YR
Value: 5, 6 or 7 dry, 3, 4 or 5 moist
Chroma: 3, 4 or 6 dry, 3, 4 or 5 moist
Texture: loam, sandy loam
Reaction: Neutral to moderately alkaline
Calcium carbonate: noneffervescent to strongly effervescent
B horizon
Hue: 10YR, 7.5YR
Value: 5 or 6 dry, 3, 4 or 5 moist
Chroma: 3 or 4 dry, 3, 4 or 5 moist
Texture: fine sandy loam, sandy loam, loam (10 to 20 percent clay)
Effervescence: Slightly to violently effervescent below a depth of 10 inches as soft masses, or thin coatings on gravel
Calcium carbonate equivalent: less than 6 percent
COMPETING SERIES: These are the Chillon (T)(TX), Momoli (AZ) and Snapcan (AZ) series. Chillon and Momoli soils are very deep. Snapcan soils are moderately deep to fanglomerate, are in the Mohave Desert (MLRAs 30) receive mostly winter precipitation and are usually dry April through November.
GEOGRAPHIC SETTING: Laposa soils are on hillslopes and mountain slopes and have slopes of 10 to 75 percent. Laposa soils formed in slope alluvium from granite, gneiss, rhyolite and eolian deposits. Elevations are 400 to 3,200 feet. The climate is hot, arid and continental. Mean annual precipitation is 3 to 10 inches and the mean annual air temperature is 70 to 74 degrees F. The frost-free period is about 260 to 325 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cherioni, Carrizo, Cristobal and Ligurta soils. Carrizo soils are sandy-skeletal. Cristobal and Ligurta soils have an argillic horizon.
DRAINAGE AND PERMEABILITY: Somewhat excessively drained; rapid runoff; moderate permeability.
USE AND VEGETATION: These soils are used for wildlife habitat and limited livestock grazing. Native vegetation is creosotebush, white bursage, littleleaf paloverde, brittlebush, ocotillo, elephant tree, cholla, turkshead, and annual forbs.
DISTRIBUTION AND EXTENT: Southwestern Arizona and southeastern California. Laposa soils are moderately extensive. MLRA is 40.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Yuma County (Yuma-Wellton Area), Arizona; 1978.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from 0 to 3 inches (A horizon)
Cambic horizon - The zone from 3 to 21 inches (Bw1, Bw2 horizons)
Lithic contact - The boundary at 32 inches (2R horizon)
Classified according to Soil Taxonomy Second Edition, 1999