LOCATION ST. ELMO COEstablished Series
TAXONOMIC CLASS: Sandy-skeletal, mixed, frigid Aridic Calciustolls
TYPICAL PEDON: St. Elmo gravelly sandy loam, grassland. (Colors are for dry soil unless otherwise noted.)
A1--O to 10 inches; brown (7.5YR 5/2) gravelly sandy loam, dark brown (7.5YR 3/2) when moist; moderate, fine, granular and crumb structure; soft, very friable; 25 percent gravel; calcareous; moderately alkaline; gradual, wavy boundary. (6 to 20 inches thick)
Clca--10 to 30 inches; very pale brown, (10YR 7/3) very gravelly loamy sand, pale brown (10YR 6/3) when moist; weak, coarse, subangular blocky structure that parts to single grains; slightly hard, loose; 70 percent gravel and some cobbles; much visible secondary calcium carbonate occurring in finely divided marl-like forms; calcareous; moderately alkaline; gradual, wavy boundary. (10 to 30 inches thick)
C2ca--30 to 60 inches, pale brown (10YR 6/3) very gravelly sand, brown (10YR 5/3) when moist; single grained; loose, 70 percent gravel and some cobbles; some visible calcium carbonate accumulating on the underside of coarse fragments; calcareous; moderately alkaline.
TYPE LOCATION: Chaffee County, Colorado; approximately 200 feet north of the edge of the terrace, 300 feet west and 500 feet south of the airport hangar in Sec. 10, T. 49 N., R. 8 E.
RANGE IN CHARACTERISTICS: The St. Elmo soils typically are calcareous throughout but depth to uniformly calcareous material ranges from 0 to 4 inches in virgin areas. Depth to the calcic horizon ranges from 7 to 40 inches. Thickness of the mollic epipedon ranges from 7 to 15inches. Exchangeable sodium ranges from 0 to 15 percent in a major part of the control section. The control section is a very gravelly loamy sand or very gravelly sand and surface soils having texture finer than loamy fine sand should not be thicker than 12 inches. Rock fragments range from 35 to 85 percent by volume and are typically less than 3 inches in diameter but range up to 10 inches in diameter.
The A horizon has hue of 2.5Y through 7.5YR, value of 4 or 5 dry, 2 or 3 moist, and chroma of 1 through 3. It ranges from mildly to strongly alkaline.
The C horizon has hue of 2.5Y through 7.5YR. It ranges from moderately to very strongly alkaline and has 15 to 40 percent calcium carbonate equivalent of the fine earth.
COMPETING SERIES: These are the Keeldar and Tridell series. Keeldar soils have a sandy loam control section, and have less than 35 percent coarse fragments. Tridell soils have moderately coarse textured control sections.
GEOGRAPHIC SETTING: The St. Elmo soils are on alluvial fans and valley side slopes. Slope gradients typically range from 2 to about 12 percent. The soils formed in alluvial parent materials derived from mixed sources but are usually strongly influenced by sedimentary rock. At the type location the average annual precipitation is 12 inches with peak periods of precipitation in the spring and summer. The mean annual temperature is 44 degrees F., and the mean summer temperature is 61 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Pando soils and competing Keeldar soils. Pando soils have albic horizons and lack calcic horizons.
DRAINAGE AND PERMEABILITY: Well drained; medium to slow runoff; rapid permeability.
USE AND VEGETATION: These soils are used principally as native rangeland; however, they are irrigated to hay crops in some localities. Native vegetation is mainly sand dropseed, blue grama, three-awn, Junegrass, Indian ricegrass, and rabbitbrush.
DISTRIBUTION AND EXTENT: High mountain valleys in central Colorado. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Chaffee County, Colorado, 1974.
REMARKS: OSED scanned by NSSQA and cleaned up by Colorado. Last revised by state 8/74.