LOCATION ACOMA              NV

ACOMA SERIES

TAXONOMIC CLASS: Fine, smectitic, mesic Calcic Paleargids

TYPICAL PEDON: Acoma gravelly sandy loam--rangeland. (Colors are for dry soil unless otherwise noted.) The surface is partially covered with 25 percent gravel.

A--0 to 10 cm; brown (10YR 5/3) gravelly sandy loam, dark brown (10YR 3/3) moist; massive; soft, very friable, slightly sticky and slightly plastic; few very fine roots; few very fine interstitial and tubular pores; 20 percent gravel; neutral (pH 7.0); abrupt wavy boundary. (8 to 13 cm thick)

Bt1--10 to 23 cm; brown (7.5YR 5/4) gravelly sandy clay, dark brown (7.5YR 3/4) moist; weak coarse prismatic structure; hard, firm, moderately sticky and moderately plastic; common medium and few fine roots; common very fine tubular pores; few thin clay films on faces of peds and lining pores; 15 percent gravel; slightly alkaline (pH 7.4); clear wavy boundary.

Bt2--23 to 38 cm; brown (7.5YR 5/4) sandy clay, dark brown (7.5YR 3/4) moist; weak coarse prismatic structure; hard, firm, moderately sticky and very plastic; few very fine roots; few very fine and fine tubular pores; common thin clay films lining pores and few thin clay films on faces of peds; neutral (pH 7.1); clear wavy boundary.

Bt3--38 to 76 cm; light brown (7.5YR 6/4) gravelly sandy clay, brown (7.5YR 4/4) moist; massive; hard, firm, moderately sticky and moderately plastic; few medium roots; few fine tubular pores; common thin clay coats and bridges; 30 percent gravel; neutral (pH 7.1); clear wavy boundary. (Combined thickness of Bt horizons is 50 to 85 cm thick)

Bk--76 to 100 cm; light brown (7.5YR 6/4) very gravelly sandy clay loam, brown (7.5YR 4/4) moist; massive; slightly hard and hard, friable, moderately sticky and moderately plastic; few fine roots; common very fine interstitial and few fine tubular pores; common 2 to 5 mm thick calcium carbonate coats on the bottom of rock fragments; few 2 to 5 mm thick extremely weakly and weakly cemented calcium carbonate seams; 50 percent gravel; slightly effervescent; slightly alkaline (pH 7.8); clear wavy boundary. (19 to 40 cm thick)

2Bk--100 to 152 cm; brown (7.5YR 5/2) very gravelly sandy clay loam, dark brown (7.5YR 3/2) moist; massive; soft, very friable, slightly sticky and moderately plastic; many very fine interstitial pores; 60 percent gravel; strongly effervescent; slightly alkaline (pH 7.8).

TYPE LOCATION: Lincoln County, Nevada; approximately 1200 feet north and 1700 feet east of the southwest corner of section 2, T. 5 S., R. 70 E.; USGS Acoma 7.5 minute topographic quadrangle; latitude 37 degrees 32 minutes and 19.9 seconds N and longitude 114 degrees 8 minutes and 16.9 seconds W; UTM zone 11, 752865e, 4158502n; NAD 83.

RANGE IN CHARACTERISTICS:
Soil moisture: Usually dry, moist in winter and spring and for 10 to 20 days cumulative from July through September, due to summer convection storms. Aridic boardering xeric moisture regime.
Mean annual soil temperature: 8 to 12 degrees C.
Depth to argillic horizon: 8 to 13 cm.
Depth to calcic horizon: 58 to 98 cm.
Carbonate stage development: III

Particle-size control section - Clay content: 35 to 45 percent.
Rock fragments: 15 to 35 percent gravel.

A horizon
Hue: 10YR or 7.5YR.
Value: 4 or 5 dry.
Chroma: 3 or 4, dry or moist.
Mineralogy: 15 to 24 percent volcanic glass in the 0.02 to 2 mm fraction and averages 0.05 to 0.09 percent Al plus 1/2Fe, extracted by ammonium oxalate.

Bt horizons
Hue: 10YR or 7.5YR.
Value: 4 through 6 dry, 3 or 4 moist.
Chroma: 3 or 4, dry or moist.
Clay content: 35 to 45 percent.
Rock fragments: 10 to 35 percent.
Texture: Clay loam, clay, or sandy clay.
Mineralogy: 15 to 24 percent volcanic glass in the 0.02 to 2 mm fraction and averages 0.05 to 0.09 percent Al plus 1/2Fe, extracted by ammonium oxalate.
Structure: Weak through strong, fine through coarse, angular blocky, subangular blocky, prismatic, or massive structure.
Consistence: Moderately hard through very hard, moderately sticky or very sticky, moderately plastic or very plastic.
Reaction: Neutral or slightly alkaline.

Bk horizon
Value: 5 through 7 dry, 4 or 5 moist.
Chroma: 2 through 4, dry or moist.
Clay content: 20 to 30 percent.
Rock fragments: 35 to 65 percent mainly gravels, with some pedons containing up to 75 percent.
Consistence: Slightly hard or hard, sticky or very sticky.
Reaction: Slightly alkaline or moderately alkaline.
Carbonates: Slightly effervescent to violently effervescent.
Other features: Some pedons may have thin weakly cemented discontinuous silica lenses throughout the horizon.
Mineralogy: 12 to 24 percent volcanic glass in the 0.02 to 2 mm fraction and averages 0.01 to 0.09 percent Al plus 1/2Fe, extracted by ammonium oxalate.

2Bk horizon
Value: 5 or 6 dry, 3 through 5 moist.
Chroma: 2 through 4, dry or moist.
Clay content: 20 to 30 percent.
Texture: Sandy clay loam, clay loam, or silt loam.
Rock fragments: 35 to 80 percent gravel.
Consistence: Soft or slightly hard, very friable or friable; slightly sticky or moderately sticky and slightly plastic or moderately plastic.
Reaction: Slightly alkaline or moderately alkaline.
Carbonates: Finely disseminated secondary calcium carbonate throughout the horizon, with 1 to 2 mm calcium carbonate concreations on the bottom of rock fragments and faces of peds in some pedons.
Mineralogy: 10 to 20 percent volcanic glass in the 0.02 to 2 mm fraction and averages 0.01 to 0.05 percent Al plus 1/2Fe, extracted by ammonium oxalate.

COMPETING SERIES: These are the Mizpah soils. Mizpah soils formed in mixed alluvium over a siltstone paralithic contact at 50 to 100 cm.

GEOGRAPHIC SETTING: Acoma soils are on eroded fan remnants. These soils formed in alluvium from welded tuff and mixed lacustrine deposits. Slopes are 2 to 15 percent. Elevations are 1,600 to 2,050 meters. The climate is cool continental. The mean annual precipitation is 200 to 300 mm; the mean annual temperature is 7 to 11 degrees C., and the frost-free season is 100 to 130 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Decan and Uana series. Decan and Uana soils have a Mollic epipedon over a duripan.

DRAINAGE AND PERMEABILITY: Well drained; slow or medium runoff; slow permeability; moderately low saturated hydraulic conductivity.

USE AND VEGETATION: Acoma soils are used for livestock grazing and wildlife habitat. The potential native vegetation is Wyoming big sagebrush, cliffrose, buckwheat, astagalus, blue grama, Indian ricegrass, bottlebrush squirreltail, and some invaded Utah juniper and singleleaf pinyon pine. This pedon is correlated to ecological site R029XY006NV, Loamy 8-10 P.Z.

DISTRIBUTION AND EXTENT: East-central Nevada. These soils are of small extent. MLRA 29.

MLRA OFFICE RESPONSIBLE: Reno, Nevada

SERIES ESTABLISHED: Lincoln County (Meadow Valley Area), Nevada, 1971.

REMARKS: Before 2009 the original classification of Acoma series was Xeric Paleargids.

Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from the surface to 10 cm (A horizon).
Abrupt boundary - An increase of 20 percent clay in a vertical distance of 2.5 cm of the upper boundary of the argillic horizon.
Argillic horizon - The zone from 10 to 76 cm (Bt1, Bt2 and Bt3 horizons).
Calcic horizon - The zone from 76 to 100 cm (BK horizon).
Particle-size control section - The zone from 10 to 60 cm (Bt1, Bt2 and part of the Bt3 horizons).