LOCATION TWINGOLD CA

Established Series
GMW/LJL/MEB
02/2025

TWINGOLD SERIES

The Twingold series consists of deep to bedrock, well drained soils that formed in residuum weathered from granitoid. The Twingold soils are on hills. Slopes range from 15 to 60 percent. The mean annual precipitation is about 200 mm, and the mean annual temperature is about 14 degrees C.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, thermic Ustic Haplargids

TYPICAL PEDON: Twingold gravelly loamy sand, on a southeast facing, 25 percent slope under rangeland at an elevation of 1444 meters. (Colors are for dry soils unless otherwise noted. 3/12/2014 actual site observation date.) The soil surface is covered by approximately 5 percent fine gravel, 10 percent medium and coarse gravel, 20 percent cobbles, 25 percent stones, 5 percent boulders.

A--0 to 4 cm (0 to 2 inches); pale brown (10YR 6/3) gravelly loamy sand, very dark grayish brown (10YR 3/2), moist; weak thick platy structure; soft, very friable, nonsticky and nonplastic; common very fine roots throughout; common very fine irregular pores; 6 percent fine gravel, 6 percent medium and coarse gravel, 5 percent cobbles; slightly alkaline (pH 7.8); abrupt smooth boundary. (3 to 7 cm thick)

Bw--4 to 10 cm (2 to 4 inches); brown (10YR 5/3) gravelly sandy loam, brown (10YR 4/3), moist; weak medium subangular blocky structure; soft, very friable, nonsticky and nonplastic; common very fine roots throughout; common very fine irregular pores; 8 percent fine gravel, 12 percent medium and coarse gravel, 5 percent cobbles; moderately alkaline (pH 8.0); abrupt smooth boundary. (5 to 20 cm thick)

Bt--10 to 34 cm (4 to 13 inches); brown (7.5YR 5/4) gravelly sandy loam, brown (7.5YR 4/4), moist; weak coarse subangular blocky structure; moderately hard, very friable, moderately sticky and slightly plastic; few coarse roots throughout and common very fine roots throughout; common very fine irregular pores; 10 percent distinct brown (7.5YR 4/4), dry, clay films on all faces of peds and 50 percent distinct brown (7.5YR 4/4), dry, clay bridges between sand grains; 18 percent fine gravel, 2 percent medium and coarse gravel; slightly alkaline (pH 7.6); gradual smooth boundary. (20 to 50 cm thick)

Ct1--34 to 80 cm (13 to 31 inches); light brown (7.5YR 6/4) gravelly coarse sand, brown (7.5YR 5/4), moist; massive; moderately hard, friable, nonsticky and nonplastic; common medium roots throughout; 50 percent distinct brown (7.5YR 4/4), dry, clay bridges between sand grains; 15 percent fine gravel, 1 percent medium and coarse gravel; slightly alkaline (pH 7.4); gradual wavy boundary.

Ct2--80 to 125 cm (31 to 49 inches); light brown (7.5YR 6/4) gravelly sand, brown (7.5YR 5/4), moist; massive; moderately hard, friable, nonsticky and nonplastic; 20 percent distinct dark yellowish brown (10YR 4/4) clay films on rock fragments; 18 percent fine gravel, 2 percent medium and coarse gravel; slightly alkaline (pH 7.4); gradual wavy boundary. (Combined thickness of the Ct horizons is 50 to 100 cm.)

Cr--125 to 150 cm (49 to 59 inches); granitoid bedrock (fractures 45 to 100 cm apart); moderately coherent.

TYPE LOCATION: San Bernardino County, California; about 4 miles northeast of Hole-in-the-Wall Fire Center on the southeast side of Twin Buttes; 650 feet west and 1930 feet north of the southeast corner of section 27, T. 12 N., R. 15 E., San Bernardino Baseline and Meridian; USGS Woods Mountains, California 7.5 minute topographic quadrangle; 35 degrees, 5 minutes, 22.90 seconds north latitude and 115 degrees, 21 minutes, 6.30 seconds west longitude; UTM zone 11 650247e, 3884232n, NAD83.

RANGE IN CHARACTERISTICS:
Soil moisture: Usually dry, moist in some part from December to March and intermittently moist for 10 to 20 days during July to September following summer convection storms; aridic moisture regime that borders on ustic.

Soil temperature: 15 to 18 degrees C
Depth to argillic horizon: 10 to 25 cm
Depth to base of argillic horizon: 30 to 75 cm
Depth to paralithic contact: 100 to 150 cm

Control section
Rock fragments: 10 to 35 percent, mainly gravel
Clay content: 12 to 18 percent

A horizon
Value: 5 or 6 dry, 3 or 4 moist
Chroma: 3 or 4 dry, 2 through 4 moist
Clay content: 2 to 8 percent
Rock fragments: 15 to 35 percent

Bw horizon
Chroma: 3 or 4 dry
Texture of the fine earth: sandy loam, fine sandy loam
Clay content: 5 to 12 percent
Rock fragments: 15 to 35 percent

Bt horizon(s)
Hue: 7.5YR or 10YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 3 or 4 moist
Texture of the fine earth: sandy loam, fine sandy loam
Clay content: 12 to 18 percent
Rock fragments: 10 to 35 percent

C or Ct horizon(s)
Chroma: 3 or 4 dry or moist
Texture of the fine earth: coarse sand, sand,
Clay content: 0 to 6 percent
Rock fragments: 15 to 35 percent

COMPETING SERIES: These are the Devamine, Diaspar and Summerford series. Devamine, Diaspar and Summerford soils are very deep. Summerford soils have secondary calcium carbonate accumulations in the profile and are in MLRA 41. Summerford soils are in MLRA 42.

GEOGRAPHIC SETTING: The Twingold soils are on hills. Slopes range from 15 to 60 percent. The soils formed in residuum weathered from granitoid. Elevation ranges from 1250 to 1500 meters. The mean annual precipitation is 175 to 250 mm. The mean annual temperature is about 13 to 16 degrees C. The frost-free period is 210 to 270 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Barnetmine, Cetrepas, and Vallegold soils. Barnetmine soils are very shallow and shallow to bedrock, have a loamy-skeletal control section and do not have an argillic horizon. Cetrepass soils are very shallow and shallow to bedrock and have a loamy-skeletal control section. Vallegold soils are shallow to bedrock and averages 18 to 30 percent clay in the particle-size control section.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained; medium runoff; high saturated hydraulic conductivity in the upper part and moderately low in the bedrock substratum.

USE AND VEGETATION: Twingold soils are used for recreation and wildlife habitat. Native vegetation is blackgrama, Virgin River brittlebush, Mohave yucca, and blackbrush.

DISTRIBUTION AND EXTENT: Mojave Basin and Range of California, U.S.A.; MLRA 30. The series is of small extent.

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Davis, California.

SERIES PROPOSED: San Bernardino County, California, Soil Survey of Mojave National Preserve Area, California, 2023. The name is coined from Twin Buttes and Gold Valley.

REMARKS: Diagnostic horizons and features in this pedon include:

Ochric epipedon - the zone from 0 to 10 cm. (A and Bw horizons)
Argillic horizon - the zone from 10 to 34 cm. (Bt horizon)
Paralithic contact - the zone from 125 to 150 cm. ((Cr horizon)
Particle size control section - the zone from 10 to 34 cm. (Bt horizon)

ADDITIONAL DATA: NASIS User Site ID: 2014CA0712015.

National Cooperative Soil Survey
U.S.A.