LOCATION POTOSI NV

Established Series
Rev. LJL/TM/JVC/ET
02/2019

POTOSI SERIES

The Potosi series consists of very shallow and shallow, well drained soils that formed in residuum and colluvium derived from limestone. Potosi soils are on mountains. Slope ranges from 15 to 50 percent. The mean annual precipitation is about 230 millimeters (9 inches) and the mean annual air temperature is about 12 degrees C. (53 degrees F.).

TAXONOMIC CLASS: Loamy-skeletal, carbonatic, mesic Lithic Torriorthents

TYPICAL PEDON: Potosi extremely gravelly loam - range and wildlife habitat. Colors are for dry soil unless otherwise noted. The soil surface is covered by approximately 75 percent gravel, 5 percent cobbles, 3 percent stones.

A--0 to 5 centimeters (0 to 2 inches); pale brown (10YR 6/3) extremely gravelly loam, dark yellowish brown (10YR 4/4) moist; moderate fine and medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; common very fine roots; many very fine and few fine tubular pores; 65 percent gravel, 3 percent cobbles, 1 percent stones; strongly effervescent; moderately alkaline (pH 8.2); abrupt smooth boundary. (3 to 8 centimeters thick)

Bk1--5 to 18 centimeters (2 to 7 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; common very fine and fine and few medium roots; common very fine and few fine tubular pores; 60 percent gravel, 5 percent cobbles; many calcium carbonate coats on undersides of rock fragments; violently effervescent; moderately alkaline (pH 8.2); clear smooth boundary. (10 to 18 centimeters thick)

Bk2--18 to 28 centimeters (7 to 11 inches); light yellowish brown (10YR 6/4) extremely gravelly sandy loam, brown (10YR 5/3) moist; weak fine subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many very fine and few fine and medium roots; few fine and many very fine interstitial and tubular pores; few fine soft masses of calcium carbonate; 70 percent gravel, 5 percent cobbles; many calcium carbonate coats on undersides of rock fragments; violently effervescent; moderately alkaline (pH 8.4); abrupt wavy boundary. (0 to 13 centimeters thick)

R--28 centimeters (11 inches); fractured limestone bedrock; few fine roots and common thin calcium carbonate coats in fractures.

TYPE LOCATION: Clark County, Nevada; about 5.6 kilometers (3.5 miles) west of Goodsprings and 8 miles south of Potosi Mountain; 235 meters (800 feet) north and 1,525 meters (5,000 feet) west of the southeast corner of sec. 20, T. 24 S., R. 58 E.; USGS Shenandoah Peak, NV 7.5 minute quadrangle; 35 degrees, 50 minutes, 27 seconds north latitude and 115 degrees, 30 minutes, 16 seconds west longitude; UTM 11, 635195e, 3967098n; NAD 83.

RANGE IN CHARACTERISTICS:

Soil moisture: Usually dry, moist in some part for short periods during winter and early spring and for 10 to 20 days cumulative between July to October following convection storms. The soils have a typic-aridic soil moisture regime.

Soil temperature: 12 to 14 degrees C. (53 to 58 degrees F.).

Depth to lithic contact: 20 to 36 centimeters (8 to 14 inches).

Calcium carbonate equivalent in the fine earth fraction: 15 to 30 percent; 40 to 60 percent in the less-than-20-millimeter fraction.

Control section
Percent clay: 8 to 15 percent.
Rock fragments: 50 to 80 percent, 50 to 70 percent gravel, and 0 to 10 percent cobbles and stones.
A horizon:
Value: 6 or 7 dry, 4 or 5 moist.

Bk horizons:
Value: 6 or 7 dry, 4 or 5 moist.
Chroma: 3 or 4.
Texture: Loam or sandy loam.
Structure: Weak, fine or medium subangular blocky.
Consistence: Nonsticky or slightly sticky and nonplastic or slightly plastic.
Identifiable secondary carbonates: Few through many thin calcium carbonate coats and pendants on rock fragments. Few or common fine soft masses of calcium carbonate in the lower Bk horizon. The zone containing more than 5 percent (by volume) identifiable secondary calcium carbonates is less than 15 centimeters (6 inches) thick and does not qualify as a calcic horizon.

COMPETING SERIES: These are the Koynik (NV), Sheeppass (NV), and Theriot (NV) series. Koynik soils have mean annual soil temperature of 8 to 11 degrees C. (47 to 52 degrees F.), 35 to 50 percent rock fragments, and 15 to 25 percent clay in the particle-size control section. Koynik soils are not moist in some part for short periods between July and October due to rain from convective storms. Sheepass soils have more than 30 percent calcium carbonate equivalence in the fine earth fraction. Theriot soils have dominantly cobbles or stones and have less than 50 percent gravel in the particle-size control section.

GEOGRAPHIC SETTING: Potosi soils are on mountains. They formed in residuum and colluvium derived from limestone. Slope ranges from 15 to 50 percent. Elevations are 1,350 to 2,180 meters (4,430 to 7,150 feet). The climate is warm-arid with cool, moist winters and hot, dry summers. The mean annual precipitation is 200 to 250 millimeters (8 to 10 inches), the mean annual air temperature is 8 to 13 degrees C. (46 to 56 degrees F.), and the frost-free period is 130 to 180 days.

GEOGRAPHICALLY ASSOCIATED SOILS: This is the Boxspring and Zeheme soils. Boxspring soils have an aridic bordering on ustic soil moisture regime. Zeheme soils are loamy-skeletal, have calcic horizons, and have a thermic soil temperature regime.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained; high surface runoff; moderate permeability; moderately high saturated hydraulic conductivity.

USE AND VEGETATION: These soils are used for range and wildlife habitat. The present vegetation is mainly blackbrush, desert needlegrass and green ephedra.

DISTRIBUTION AND EXTENT: Mojave Desert of southern Nevada; MLRA 30. These soils are not extensive.

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: PHOENIX, ARIZONA

SERIES ESTABLISHED: Clark County Area, Nevada, 2006. Proposed in Clark County, Nevada, 1994. The name is from Potosi Mountain.

REMARKS: Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - 0 to 18 centimeters (0 to 7 inches) (A and Bk1 horizons).
Lithic contact - 28 centimeters (11 inches) (R layer).
Particle-size control section - 0 to 28 centimeters (0 to 11 inches) (A, Bk1 and Bk2 horizons).

National Cooperative Soil Survey
U.S.A.