LOCATION ELGIN AZEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, thermic Calcic Paleargids
TYPICAL PEDON: Elgin very gravelly fine sandy loam - rangeland. (Colors are for dry soil unless otherwise noted.) 25 to 30 percent of the surface is covered with gravel.
A--0 to 1 inch; brown (10YR 4/3) very gravelly fine sandy loam, dark brown (10YR 3/3) moist; weak granular structure; soft, very friable, nonsticky and nonplastic; common very fine roots; common fine irregular and tubular pores; 38 percent gravel and 5 percent cobble; noneffervescent; neutral (pH 6.8); abrupt smooth boundary. (1 to 3 inches thick)
Bt1--1 to 6 inches; dark reddish brown (5YR 3/2) clay, dark reddish brown (5YR 2.5/2) moist; moderate medium angular blocky structure; slightly hard, firm, very sticky and very plastic; common very fine and fine roots; common fine tubular pores; many distinct clay films on ped faces and on rock fragments; 10 percent gravel; noneffervescent; neutral (pH 6.8); clear smooth boundary.
Bt2--6 to 15 inches; dark reddish brown (5YR 3/4) clay, dark reddish brown (5YR 3/3) moist; moderate medium angular blocky structure; slightly hard, firm, very sticky and very plastic; common very fine and fine roots; common fine tubular pores; many distinct clay films on ped faces and on rock fragments; 10 percent gravel; noneffervescent; neutral (pH 7.2); abrupt smooth boundary. (Combined thickness of the Bt horizons is 8 to 20 inches)
Btk--15 to 21 inches; reddish brown (5YR 5/4) gravelly sandy clay loam, reddish brown (5YR 4/4) moist; weak fine subangular blocky structure; slightly hard, firm, moderately sticky and moderately plastic; few very fine roots; few fine tubular pores; common distinct clay films on rock fragments; common distinct calcium carbonate coatings on rock fragments; 25 percent gravel; slightly effervescent, 11 percent calcium carbonate equivalent; slightly alkaline (pH 7.6); abrupt smooth boundary. (6 to 8 inches thick)
Bk1--21 to 27 inches; 70 percent light reddish brown (5YR 6/4) and 30 percent reddish brown (5YR 4/4) gravelly sandy loam, 70 percent pink (5YR 7/4) and 30 percent reddish brown (5YR 5/4) moist; massive; soft, friable, nonsticky and nonplastic; common fine roots; few fine irregular and tubular pores; many distinct calcium carbonate coatings on rock fragments; 30 percent gravel; violently effervescent, 11 percent calcium carbonate equivalent; moderately alkaline (pH 8.0); clear smooth boundary.
Bk2--27 to 60 inches; pinkish gray (7.5YR 7/2) very gravelly sandy loam, brown (7.5YR 5/4) moist; massive; slightly hard, friable, nonsticky and nonplastic; few fine roots; few fine irregular and tubular pores; many distinct calcium carbonate coatings on rock fragments; 40 percent gravel; violently effervescent, 20 percent calcium carbonate equivalent; moderately alkaline (pH 8.2). (Combined thickness of the Bk horizons is 35 to 45 inches)
TYPE LOCATION: Walnut Gulch Experimental Watershed, Cochise County, Arizona; located at a latitude of 31 degrees, 44 minutes, 28 seconds North and longitude of 109 degrees, 56 minutes, 30 seconds West; 2325 feet north and 350 feet west from southeast corner of section 36, T. 19 S., R. 23 E.
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. Ustic aridic soil moisture regime.
Soil Temperature: 62 to 69 degrees F.
Rock fragments: averages less than 35 percent in the particle-size control section
Depth to calcic horizon: 20 to 40 inches
Clay content: more than 35 percent
Organic Matter: 1 to 2 percent
A horizon
Hue: 7.5YR, 10YR
Value: 3 through 5 dry, 3 or 4 moist
Chroma: 2 through 4, dry or moist
Reaction: slightly acid or neutral
Effervescence: none
Bt horizon
Hue: 2.5YR, 5YR
Value: 2.5 through 5, dry or moist
Chroma: 2 through 6, dry or moist
Texture: clay loam, clay, sandy clay
Reaction: neutral to slightly alkaline
Effervescence: none
Btk horizon
Hue: 2.5YR, 5YR, 7.5YR
Value: 3 through 8, dry or moist
Chroma: 2 to 6, dry or moist
Reaction: neutral to moderately alkaline
Effervescence: slight or strong, 5 to 15 percent calcium carbonate equivalent
Texture: sandy clay loam, clay loam, clay
Bk horizon
Hue: 7.5YR, 5YR
Value: 4 through 7, dry or moist
Chroma: 2 through 6, dry or moist
Reaction: slightly to moderately alkaline
Effervescence: strong or violent, 10 to 25 percent calcium carbonate equivalent
Texture: sandy loam, loam, clay loam, coarse sandy loam, sandy clay loam
COMPETING SERIES: This is the Sparks (NM) series. Sparks soils formed in sediments from the Ogalalla Formation that have been modified by winds on nearly level plains of the Great Plains, and are moist in the soil moisture control section during May and June.
GEOGRAPHIC SETTING: Elgin soils are on fan terraces and fan piedmonts at elevations of 3,800 to 5,200 feet. Slopes range from 1 to 25 percent. These soils formed in mixed fan alluvium. The mean annual precipitation is 12 to 16 inches and occurs as thunderstorms during July to September and as gentle rains during December and January. The mean annual air temperature is 60 to 67 degrees F. The frost-free period is 180 to 250 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Stronghold and Bernardino soils. Stronghold soils are coarse-loamy. Bernardino soils do not have an abrupt textural change.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; slow permeability.
USE AND VEGETATION: Used for experimental rangeland research, livestock grazing and wildlife habitat. Vegetation includes sideoats grama, cane beardgrass, plains bristlegrass, plains lovegrass, prairie junegrass, green sprangletop, hairy grama, curly mesquite, vine mesquite, shrubby buckwheat, range ratany and false mesquite.
DISTRIBUTION AND EXTENT: Southern Arizona. Elgin soils are of moderate extent. MLRA is 41. Named derived from a town in southern Arizona.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Cochise County, Arizona; Soil survey of Cochise County, Arizona, Douglas-Tombstone Part; 1996.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from 0 to 1 inch (A horizon)
Argillic horizon - The zone from 1 to 21 inches (Bt1, Bt2, Btk horizons)
Calcic horizon - The zone from 27 to 60 inches (Bk2 horizon)
Pale feature - Abrupt textural change at 1 inch
Classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Tenth Edition, 2006.