LOCATION PLATORO COEstablished Series
TAXONOMIC CLASS: Fine-loamy over sandy or sandy-skeletal, mixed, superactive, frigid Ustic Haplargids
TYPICAL PEDON: Platoro loam - grassland. (Colors are for dry soil unless otherwise noted.)
A1--0 to 4 inches; light brownish gray (1OYR 6/2) light loam, dark grayish brown (10YR 4/2) moist; moderate fine granular structure; soft, very friable; 5 percent gravel; calcareous; moderately alkaline (pH 8.0); clear gmooth boundary. (3 to 6 inches thick)
B1-- 4 to 7 inches; light brownish gray (10YR 6/2) heavy loam, dark grayish brown (10YR 4/2) moist; weak medium subangular blocky structure that parts to moderate medium granules; slightly hard, very friable; few glossy patches on some faces of peds; 5 percent gravel, mostly basalt; many dark gray mineral grains in the sand and silt fractions; calcareous; moderately alkaline (pH 8.0); clear smooth boundary. (2 to 4 inches thick)
B2t--7 to 15 inches; brown (10YR 5/3) light clay loam, dark brown (10YR 4/3) moist; moderate medium prismatic structure that parts to moderate medium subangular blocks; slightly hard, very friable; peds are very hard; thin wax-like patches on faces of peds; thin wax-like coatings in root channels; 5 percent gravel, mostly basalt; many dark gray volcanic mineral grains in the sand and silt fractions; calcareous; moderately alkaline (pH 8.2); gradual wavy boundary. (4 to 20 inches thick)
B3ca--15 to 18 inches; brown (1OYR 5/3) light clay loam, dark brown (1OYR 4/3) moist; weak medium subangular blocky structure; hard, friable; peds are very hard; thin wax-like patches on faces of peds; discontinuous wax-like coatings in root channels; 10 percent gravel, mostly basalt; many dark colored mineral grains in the sand and silt fractions; visible secondary calcium carbonate occurring as concretions and as coatings on pebbles; calcareous; moderately alkaline (pH 8.4); gradual wavy boundary. (3 to 5 inches thick)
Clca--18 to 26 inches; brown (10YR 5/3) very gravelly loam, dark brown (10YR 4/3) moist; massive; hard, friable; 60 percent gravel, mostly basalt; many dark mineral grains in the sand and silt fractions; visible secondary calcium carbonate occurring as concretions, in thin seams and streaks, and as coatings on the pebbles; calcareous; moderately alkaline (pH 8.4); gradual wavy boundary. (4 to 25 inches thick)
IIC2ca--26 to 40 inches; very gravelly loamy sand or sand. Rock fragments are mostly basalt and there are many dark mineral grains in the sand and silt fractions; visible secondary calcium carbonate occurring as coatings on rock fragments.
TYPE LOCATION: Rio Grande County, Colorado; 400 feet east of the NW corner of Sec. 36, T. 37 N., R. 7 E.
RANGE IN CHARACTERISTICS: Mean annual soil temperature ranges from 43 to 46 degrees F., and mean summer soil temperature ranges from 62 to 65 degrees F. Exchangeable sodium ranges from 0 to 15 percent and conductivity ranges from 0 to 14 millimhos within the epipedon and the argillic horizon. Depth to uniformly calcareous material ranges from 0 to 18 inches. Depth to the sandy-skeletal IIC horizon ranges from 20 to 40 inches. Depth to the base of the argillic horizon ranges from 10 to 36 inches. Depth to continuous subhorizons of visible secondary calcium carbonate and/or sulfate accumulation ranges from 10 to 40 inches but such horizons are not strong enough to qualify as calcic or gypsic horizons. The argillic horizon averages 15 to about 35 percent fine or coarser sand. Any C horizon above the sandy-skeletal substratum ranges in clay from 18 to 35 percent and in fine or coarser sand from 15 to 35 percent. Rock fragments range from 0 to 35 percent in a major part of the solum and are mainly 1 to 10 inches in diameter.
The A horizon has hue of 5Y through 7.5YR, value of 5 or 6 dry, 4 or 5 moist, and chroma of 2 or 3. Reaction ranges from neutral to moderately alkaline.
The Bt horizon has hue of 5Y through 7.5YR, value of 5 or 6 dry, 3 or 4 moist, and chroma of 2 through 4. Reaction ranges from mildly to moderately alkaline.
The C or IIC horizon has hue of 5Y through 7.5YR, value of 5 or 6 dry, 4 or 5 moist, and chroma of 2 or 3. Reaction is mildly or moderately alkaline.
COMPETING SERIES: These are the Bosler, (T) Millburne, (T) Relsob, and Tigiwon series. Bosler soils have a calcic horizon. Millburne soils have solums less than 15 inches thick and have a calcic horizon. Relsob soils lack uniform horizons of calcium carbonate. Tigiwon soils have sand and gravel substratums at depths of 10 to 20 inches, and have solums less than 15 inches thick.
GEOGRAPHIC SETTING: Platoro soils are on alluvial fans and high terraces. Slopes range from 0 to 15 percent. These soils formed in moderately thin, calcareous, medium to moderately fine textured alluvial parent materials derived principally from basalt and overlying beds of sand and gravel. The average annual precipitation is 8 to 12 inches with peak periods of precipitation during the spring and early summer months. Mean annual temperature is 40 to 43 degrees F., mean summer temperature is 60 to 64 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the San Arcacio and Stunner soils. San Arcacio soiis have more than 0.6 percent organic carbon in the upper 16 inches. Stunner soils have a fine-loamy control section.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; moderate permeability.
USE AND VEGETATION: These soils are used as native pastureland and for irrigated cropland. Principal native plants are western wheatgrass, snakeweed, and Russian thistle.
DISTRIBUTION AND EXTENT: San Luis Valley Area of south central Colorado. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Rio Grande County Area, Colorado, 1972.
REMARKS: Last updated by the state 1/81.