LOCATION FLATIRONS COEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, smectitic, mesic Aridic Paleustolls
TYPICAL PEDON: Flatirons very cobbly sandy loam, grassland. (Colors are for dry soil unless otherwise noted.)
A1--0 to 6 inches; very dark grayish brown (10YR 3.2) very cobbly sandy loam, very dark brown (10YR 2/2) moist; moderate medium granular structure; soft, very friable, slightly sticky; 60 percent rock fragments; neutral; clear smooth boundary. (5 to 8 inches thick)
A2--6 to 13 inches; very dark grayish brown (10YR 3/2) very cobbly sandy loam, very dark grayish brown (10YR 3/2) moist; weak medium subangular blocky structure parting to moderate medium granular; soft, very friable, slightly sticky; 60 percent rock fragments; slightly acid; abrupt wavy boundary. (5 to 12 inches thick)
Bt1--13 to 21 inches; reddish brown (5YR 5/4) very gravelly clay, reddish brown (5YR 4/4) moist; strong medium prismatic structure parting to strong medium angular blocks; extremely hard, very firm, very sticky; 60 percent rock fragments; many thick clay films on faces of peds; medium acid; gradual smooth boundary. (4 to 10 inches thick)
Bt2--21 to 38 inches; strong brown (7.5YR 5/6) very gravelly sandy clay, strong brown (7.5YR 4/6) moist; strong medium prismatic structure parting to strong medium angular blocks; very hard, firm, very sticky; 60 percent rock fragments; common moderately thick clay films on faces of peds; medium acid; gradual smooth boundary. (10 to 18 inches thick)
Bt3k--38 to 47 inches; strong brown (7.5YR 5/8) very gravelly sandy clay, strong brown (7.5YR 5/6) moist; strong medium prismatic structure parting to strong medium angular blocks; hard, friable, very sticky; 60 percent rock fragments; common moderately thick clay films on faces of peds; slightly acid; gradual wavy boundary. (6 to 10 inches thick)
BC--47 to 60 inches; strong brown (7.5YR 5/8) very gravelly sandy clay loam, strong brown (7.5YR 5/6) moist; weak coarse prismatic structure parting to weak coarse subangular blocks; hard, friable, very sticky; 60 percent rock fragments; slightly acid.
TYPE LOCATION: Jefferson County, Colorado; about 8 miles north of Golden; 60 feet west and 750 feet south of NE corner of Sec. 20, T. 2 S., R. 70 W.
RANGE IN CHARACTERISTICS: The mollic epipedon ranges from 10 to 20 inches thick. The thickness of the solum ranges from 40 to 60 inches. Rock fragments range from 35 to 80 percent by volume and are commonly well rounded and range in size from 1/8 to 10 inches in diameter.
The A horizon has hues of 10YR or 7.5YR, color value of 3 through 5, 2 or 3 moist, and chroma of 2 or 3. It is dominantly very cobbly and includes stony and very stony modifiers. Reaction is slightly acid to mildly alkaline.
The Bt horizon has hues of 7.5YR through 2.5YR in the upper part and includes 10YR in the lower part, color value of 5 or 6, 3 through 5 moist and chroma of 3 through 8 with darker colors in upper part. It is dominantly very gravelly sandy clay, very gravelly clay loam or very gravelly clay with a range in clay of 35 to 60 percent. Reaction is neutral to medium acid.
The C horizon when present has hues of 10YR through 2.5YR. It is dominantly a coarse sandy clay loam including cobbly loams.
COMPETING SERIES: These are the Signal and Veldkamp series in other families. Signal soils have thermic temperatures. Veldkamp soils do not have an abrupt textural change from the A to the Bt horizon.
GEOGRAPHIC SETTING: Flatirons soils are on pediments, high terraces, and side slopes. Slopes range from 0 to 30 percent. Elevations range from 5,600 to 6,500 feet. The soils formed in very gravelly and cobbly loamy stratified old alluvium derived from sedimentary, metamorphic and igneous rocks. The average annual precipitation ranges from 16 to 19 inches. The mean annual temperature is about 47 degrees F. The frost-free season is 125 to 142 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Veldkamp soils, and the Nederland, Willowman and Valmont soils. The Nederland and Willowman soils are loamy- skeletal. Valmont soils have contrasting textures within the series control section.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; slow permeability.
USE AND VEGETATION: Soils are used for grazing, wildlifem and community development. Native vegetation is mainly blue grama, little bluestem, mountain muhly, switch grass, big bluestem, western wheatgrass, and forbs.
DISTRIBUTION AND EXTENT: Foothills area of north central Colorado. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Golden Area Soil Survey, Jefferson County, Colorado, 1980.