LOCATION PLOMOSA AZ

Tentative Series
WAS/NMS
08/2018

PLOMOSA SERIES

The Plomosa series consists of moderately deep, somewhat excessively drained soils formed in slope alluvium, colluviums, and or residuum derived from igneous and metamorphic rocks. Plomosa soils are on hills and mountains and have slopes of 3 to 70 percent. The mean annual precipitation is about 7 inches and the mean annual air temperature is about 72 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, hyperthermic Typic Haplocalcids

TYPICAL PEDON: Plomosa gravelly loam - rangeland. (Colors are for dry soil unless otherwise noted.) 80 to 90 percent of surface covered with gravel and cobbles.
A--0 to 2 inches; brown (7.5YR 5/4) gravelly loam, brown (7.5YR 4/4) moist); 12 percent clay; moderate medium and thick platy parting to moderate fine granular structure; soft, very friable, slightly sticky, slightly plastic; many very fine and few fine roots; many very fine tubular and irregular pores; 25 percent gravel; strongly effervescent, 6 percent calcium carbonate equivalent; moderately alkaline (pH 8.0) clear wavy boundary. (2 to 4 inches thick)

Bkk1--2 to 9 inches; light brown (7.5YR 6/4) very gravelly sandy loam, brown (7.5YR 5/4) moist; 14 percent clay; weak medium subangular blocky parting to moderate medium granular structure; soft, very friable, slightly sticky and nonplastic; many very fine roots; many very fine tubular and irregular pores; many patchy distinct carbonate coats on rock fragments and many fine and medium calcium carbonate masses; 55 percent gravel; violently effervescent, 28 percent calcium carbonate equivalent; moderately alkaline (pH 8.0); abrupt wavy boundary. (6 to 15 inches thick)

Bkk2--9 to 38 inches; light brown (7.5YR 6/4) extremely gravelly sandy loam, brown (7.5YR 5/4) moist; 12 percent clay; massive; soft, very friable, slightly sticky and nonplastic; many very fine roots; many very fine irregular pores; common continuous distinct carbonate coats on rock fragments; many fine threadlike carbonate masses and few fine carbonate nodules;75 percent gravel; violently effervescent, 11 percent calcium carbonate equivalent; moderately alkaline (pH 8.0); abrupt wavy boundary. (10 to 25 inches thick)

R--38 to 60 inches; highly fractured igneous bedrock.

TYPE LOCATION: La Paz County, Arizona; USGS, Ibex Peak, 7.5 minute topographic quadrangle; located 990 feet south and 1,500 feet west of the northeast corner of section 6, T. 5 N., R. 17 W. Latitude 33 degrees, 48 minutes, 32 seconds N., Longitude of 114 degrees, 03 minutes, 59 seconds W., NAD83.

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.
Mean Annual Soil Temperature: 70 to 78 degrees F.
Rock fragments: 35 to 80 percent
Reaction: slightly to moderately alkaline
Average percent clay in the control section: 7 to 20
Calcium carbonate equivalent: 5 to 40 percent
Depth to calcic horizon: 2 to 20 inches
Depth to bedrock: 20 to 40 inches

A horizon
Hue: 10YR, 7.5YR
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 3 or 4, dry or moist
Texture: sandy loam, loam, fine sandy loam

Bk horizons
Hue: 10YR, 7.5YR
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 3 or 4, dry or moist
Texture: sandy loam, loam, fine sandy loam

COMPETING SERIES: These are the Gunsight (AZ), Chemehuevi (CA), Heleweiser (NV), Oldswede (T)(CA), and Supplymine(CA) series. Gunsight, Chemehuevi, Heleweiser and Oldswede soils are very deep. Supplymine soils occur in MLRA 30.

GEOGRAPHIC SETTING: Plomosa soils are on hills and mountains and have slopes of 3 to 70 percent. Plomosa soils formed in slope alluvium, colluviums, and or residuum derived from igneous and metamorphic rocks. Elevations range from 1,000 to 3,000 feet. The climate is hot, arid and continental. The mean annual precipitation is 2 to 10 inches and the mean annual air temperature is 70 to 76 degrees F. The frost-free period is about 260 to 340 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Chuckawalla, Gunsight, Guvo, Hickiwan, and Rillito soils. Chuckawalla soils have argillic horizons and are located on fan piedmonts. Gunsight soils are very deep and are located on fan piedmonts. Guvo soils contain petrocalcic horizons underlain with bedrock and are located on hills, mountains and fan piedmonts. Hickiwan soils contain petrocalcic horizons and are located on fan piedmonts. Rillito soils have 15 to 35 percent gravel and are very deep and are located on fan piedmonts and alluvial fans.

DRAINAGE AND PERMEABILITY: Somewhat excessively drained; medium to high runoff; moderate or moderately rapid permeability.

USE AND VEGETATION: These soils are used for wildlife habitat, recreation and limited livestock grazing. Native vegetation is creosote bush, white bursage, little leaf paloverde, brittlebush, ocotillo, cholla, and ironwood.

DISTRIBUTION AND EXTENT: Southwestern and south central Arizona. Plomosa soils are moderately extensive. MLRA 40.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona

SERIES PROPOSED: La Paz County, Arizona: Soil Survey of Kofa Area, Arizona, Parts of La Paz and Yuma Counties.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from 0 to 2 inches (A horizon)
Calcic horizon - The zone from 2 to 38 inches (Bkk1, Bkk2 horizons)
Lithic contact - The boundary at 38 inches (R horizon)
Classified according to Soil Taxonomy; Keys to Soil Taxonomy, Twelfth edition, 2018.
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National Cooperative Soil Survey
U.S.A.