LOCATION EARP AZ+NMEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic Aridic Argiustolls
TYPICAL PEDON: Earp very gravelly loam - rangeland. (Colors are for dry soil unless otherwise noted.)
A--0 to 2 inches; dark grayish brown (10YR 4/2) very gravelly loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure; hard, friable, slightly sticky, slightly plastic; many fine roots; many fine interstitial pores; more than 35 percent fine, medium and large angular and subangular pebbles; noneffervescent; slightly alkaline (ph 7.5); abrupt smooth boundary. (1 to 4 inches thick)
Bt1--2 to 8 inches; dark brown (7.5YR 3/2) very gravelly clay loam, dark reddish brown (5YR 2/2) moist; moderate fine and medium subangular blocky parting to moderate fine granular structure; hard, friable, sticky, plastic; many fine roots; many fine interstitial and few fine tubular pores; more than 50 percent fine, medium and large angular and subangular pebbles; noneffervescent; moderately alkaline (pH 8.0); clear wavy boundary. (5 to 9 inches thick)
Bt2--8 to 25 inches; dark brown (7.5YR 3/2) very gravelly clay loam, very dark brown (10YR 2/2) moist; moderate fine and medium subangular blocky structure; hard, friable, sticky, plastic; common fine roots; many fine interstitial pores; more than 50 percent medium and large pebbles and few cobbles, both angular and subangular; moderately effervescent; moderately alkaline (pH 8.0); gradual wavy boundary. (8 to 20 inches thick)
Ckm--25 to 40 inches; pale brown (10YR 6/3) weakly cemented angular and subangular pebbles, cobbles and stones, brown (10YR 5/3) moist; massive; extremely hard; very pale brown (10YR 8/2) spots and veins of lime; few fine roots; strongly effervescent; moderately alkaline (pH 8.0).
TYPE LOCATION: Cochise County, Arizona; approximately 17 miles southeast of Willcox, Arizona along State Highway 186; approximately 800 feet north of SE corner sec. 5, T.15S., R.27E.
RANGE IN CHARACTERISTICS:
Soil moisture: Aridic ustic moisture regime
Depth to the C horizon ranges from 20 to 36 inches.
Rock fragments: Pebbles, cobbles and stones range from 35 to 50 percent by volume and rock fragments increase as depth increases.
A and Bt1 horizons
Hue: 7.5YR, ranging from 5YR to 10YR,
Value: less than 5 dry, 2 or 3 moist
Chroma: of 2 through 4.
Reaction: A horizon is slightly acid to slightly alkaline.
Bt2 horizon
Texture: clay loam textures with 30 to 35 percent clay.
Reaction: slightly to moderately alkaline
Effervescence: noneffervescent throughout in some pedons.
COMPETING SERIES: These are the Eicks (NM) and Hurds (TX) series. Eicks soils have A1 horizons more than 10 inches thick and have mottled B22t horizons with hue of 10YR or 2.5Y. Hurds soils have slightly acid or medium acid B2t horizons with lamellae.
GEOGRAPHIC SETTING: The Earp soils are on deeply dissected, moderately sloping to moderately steep old alluvial fans at elevations ranging from 4,000 to 6,000 feet. Dominant slopes are 5 to 30 percent. These soils formed in cobbly and gravelly coarse-textured old valley filling materials from quartzite, andesite, and granite with some dolomitic marble. The average annual precipitation is 12 to 16 inches, about 1/2 of which comes as summer thundershowers in July, August, and September. The mean annual temperature is 58 degrees to 65 degrees F. and the frost-free season is 155 to 175 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Grabe, Kimbrough, and White House soils. Grabe soils are dark colored, deep loamy soils that lack a B horizon and rock fragments. Kimbrough soils lack a B horizon and have a petrocalcic horizon at shallow depths. White House soils have fine textured B horizons and contain less than 35 percent rock fragments.
DRAINAGE AND PERMEABILITY: Well-drained; medium runoff; moderately slow permeability.
USE AND VEGETATION: Used as rangeland. Semi-desert grassland; principal species are sideoats grama, slender grama and black grama, three-awn, and annual grasses.
DISTRIBUTION AND EXTENT: Southeastern Arizona and southern New Mexico. Earp soils are moderately extensive. MLRAs 41 & 42.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Desert Soil Geomorphology Project, New Mexico, 1973.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from 0 to 8 inches (A & Bt1 horizons)
Argillic horizon - The zone from 8 to 25 inches (Bt2 horizons)
Classified according to Keys to Soil Taxonomy Tenth Edition, 2006
This series represents an identified soil in the Jornada Experimental Range near the Desert Soil-Geomorphology Project, Las Cruces, New Mexico. The project was a study of soils and geomorphology in an arid and semi-arid environment. The series is extensively referenced in many documents, publications and thesis. Revision and use outside the project area is discouraged in order to preserve the historical concept for research.