LOCATION FALLSAM NM+AZEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, smectitic, mesic Pachic Argiustolls
TYPICAL PEDON: Fallsam cobbly silt loam, rangeland. (Colors are for air dry soil unless otherwise noted.)
A--0 to 5 inches; dark grayish brown (10YR 4/2) cobbly silt loam, very dark grayish brown (10YR 3/2) moist; weak fine subangular blocky structure; soft, friable, slightly sticky, plastic; many fine roots; 20 percent basalt cobbles and gravel; neutral; clear irregular boundary. (0 to 10 inches thick)
Bt1--5 to 9 inches; brown (10YR 4/3) cobbly silty clay loam, dark brown (10YR 3/3) moist; moderate fine subangular blocky and blocky structure; hard, friable, sticky, plastic; common fine roots; few thin clay films; 30 percent basalt cobbles and gravel; neutral; abrupt irregular boundary. (3 to 8 inches thick)
Bt2--9 to 35 inches; brown (10YR 5/3) very cobbly clay, dark brown (10YR 3/3) moist; strong fine blocky structure; very hard, firm, sticky, plastic; few fine roots; many thin clay films on faces of peds and on rock fragments; 70 percent basalt cobbles and gravel; neutral; gradual irregular boundary. (14 to 35 inches thick)
Bk--35 to 46 inches; brown (7.5YR 5/4) very cobbly clay, brown (7.5YR 4/4) moist; strong fine granular structure; hard, firm, slightly sticky, slightly plastic; 75 percent, increasing with depth to 90 percent, basalt gravel, cobbles, and stones; a few thin lime coatings on bottom of stones; neutral.
TYPE LOCATION: Union County, New Mexico; 2.0 miles north of 1.5 miles east of the headquarters of Capulin National Monument, 2,600 feet west and 2,450 feet south of the NE corner sec. 27, T.30N., R.28E.
RANGE IN CHARACTERISTICS:
Depth to consolidated bedrock: is more than 40 inches.
Reaction: Usually the profile is neutral; some pedons are slightly calcareous and slightly alkaline below a depth of 30 inches.
Soil temperature: 47 degrees to 54 degrees F.
Soil moisture: The moist control section is dry in some part during most of the late fall and winter months. It is moist in some part during the majority of the 150 day growing season in which about 2/3 of the 16 inch rainfall is received. Aridic ustic moisture regime.
A horizon
Value: 3 or 4 dry, 2 or 3 moist
Chroma: 1 through 3
Texture: silt loam, loam or silty clay loam
Rock fragments: 5 to 80 percent, less than 25 percent of these are gravel.
Bt horizon
Hue: 7.5YR or 10YR
Value (upper part): 3 through 5 dry, 2 or 3 moist
Chroma upper part): 2 or 3. Value (below 25 inches): 4 through 6 dry, 3 or 4 moist
Chroma (below 25 inches):3 or 4
Texture: clay or silty clay
Clay content: 35 to 50 percent clay
Rock fragments: 50 to 90 percent rock fragments, less than 25 percent of these are gravel.
Clay films are present on faces of peds and rock fragments.
Bk horizon
Rock fragments: 70 to 95 percent rock fragments and it commonly grades into consolidated bedrock at depths of 40 to 80 inches. Less than 25 percent of the rock fragments are gravel.
Texture: silty clay loam or clay.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Fallsam soils are on gently sloping basalt flows around the base of volcanic cones or vents. Elevations range from 6,400 to 7,800 feet. The landscape includes a series of stony ridges of "squeeze ups" with flat areas between them. Fallsam soils occur around the base of the stony ridges. The soils formed in fine textured materials mixed with basalt fragments ranging in size from gravel to boulders. Annual temperature at the type location is 46 degrees F., the annual precipitation is 15 to 18 inches, and the Thornthwaite P-E Index is 26.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Apache and Capulin soils and the competing La Brier and Torreon soils. Apache soils have a lithic contact at depths of less than 20 inches. Capulin soils lack pachic epipedons and skeletal control sections.
DRAINAGE AND PERMEABILITY: Well-drained; slow runoff; slow permeability.
USE AND VEGETATION: This soil is used as rangeland and wildlife habitat. Principal plants are blue grama, sideoats grama, western wheatgrass, squawbush, and juniper.
DISTRIBUTION AND EXTENT: Northeast New Mexico and southeast Arizona. This series is of moderate extent. MLRAs 70A & 41. Use of this series in MLRA 41 should be discontinued.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Union County, New Mexico, 1972.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from 0 to 35 inches (A & Bt horizons)
Argillic horizon - The zone from 9 to 35 inches (Bt horizons)
Classified according to Keys to Soil Taxonomy Tenth Edition, 2006
The series classification might better fit a Torrertic Argiustoll. The rock fragments make it difficult to evaluate shrink-swell in the field and laboratory data are not available. The mineralogy is assumed to be montmorillonitic based on the mineralogy of similar soils.