LOCATION CORTA COEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Udertic Paleustalfs
TYPICAL PEDON: Corta loam, open forest. (Colors are for dry soil unless otherwise noted.)
A--0 to 4 inches; grayish brown (10YR 5/2) silt loam, very dark grayish brown (10YR 3/2) moist; strong fine granular structure; soft, friable, slightly sticky, slightly plastic; slightly acid; abrupt smooth boundary. (2 to 8 inches thick)
Bt--4 to 31 inches; brown (7.5YR 5/4) clay, dark brown (7.5YR 4/4) moist; weak very coarse prismatic structure parting to moderate coarse angular blocks; wide cracks between peds when dry; slightly hard, friable, sticky, plastic; peds are extremely hard; common clay films on faces of peds, in root channels and in pores; common slickensides; slightly acid; gradual wavy boundary. (5 to 35 inches thick)
BC--31 to 36 inches; brown (7.5YR 5/4) clay, dark brown (7.5YR 4/4) moist; weak coarse angular blocky structure; cracks between peds when dry; hard, firm, sticky, plastic; peds are extremely hard, few thin clay films on faces of peds and discontinuous clay films in root channels; neutral; gradual wavy boundary. (3 to 8 inches thick)
C--36 to 50 inches; light yellowish brown (10YR 6/4) clay, yellowish brown (10YR 5/4) moist; massive; cracks develop erratically when dry; extremely hard, very firm, sticky, plastic; common small shale chips; mildly alkaline.
Cr--50 inches; shale.
TYPE LOCATION: LaPlata County, Colorado; NE1/4 section 34, T.35N., R.6W.
RANGE IN CHARACTERISTICS: Depth to uniformly calcareous material ranges from 40 to more than 60 inches but should not be shallower than the upper 3 inches of the C horizon if the solum is thicker than 37 inches. Depth to a paralithic contact ranges from 40 to 60 inches. Mean annual soil temperature is 48 to 51 degrees F., and mean summer soil temperature is 60 to 64 degrees F. Thin discontinuous E horizons may occur in some pedons.
The A horizon has hue of 5Y through 7.5YR, value of 5 through 7 dry, 3 through 6 moist, and chroma of 1 through 4. It is medium through neutral.
The Bt horizon has hue of 5Y through 5YR, value of 5 through 7 dry, 4 through 6 moist, and chroma of 1 through 6. It is typically clay loam, clay and silty clay loam with over 35 percent clay. This horizon is medium acid through neutral.
The C horizon has hue of 5Y through 7.5YR, hue of 6 or 7, 5 or 6 moist and chroma of 3 through 6. It is typically clay or silty clay loam and has 35 to 50 percent clay. This horizon is slightly acid through mildly alkaline.
COMPETING SERIES: There are no other series in this family. A similar soil is the Ulm series, Ulm soils lack on abrupt textural boundary and are calcareous above 40 inches.
GEOGRAPHIC SETTING: The Corta soils are on mesa tops, ridgetops, and old pediment surfaces. Slopes range from 4 to 75 percent. These soils formed in thick, noncalcareous, fine textured materials derived principally from sedimentary bedrocks. At the type location the mean annual precipitation is 20 to 25 inches. Mean annual temperature is 45 to 48 degrees F., and mean summer temperature is 58 to 62 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Carracas soils and competing Ulm soils. Carracas soils lack a Bt horizon and have bedrock above 20 inches.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; very slow permeability.
USE AND VEGETATION: Used as native pastureland. Native vegetation is mainly ponderosa pine and oakbrush, with an understory of grass and shrubs.
DISTRIBUTION AND EXTENT: Southwestern Colorado. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: LaPlata County (Piedra Area), Colorado, 1974.