LOCATION ATLATL NM+AZ COEstablished Series
TAXONOMIC CLASS: Coarse-loamy, carbonatic, mesic Aridic Calciustepts
TYPICAL PEDON: Atlatl gravelly fine sandy loam -- on a stable plateau rim sloping 2 percent to the east at 6,670 feet elevation -- woodland. (Colors are for dry soil unless otherwise noted. When first described, the soil was dry from the surface to depth of 2 inches and moist from 2 inches to the bedrock contact at 30 inches.)
A--0 to 2 inches; brown (7.5YR 5/4) gravelly fine sandy loam, brown (7.5YR 4/4) moist; moderate medium platy structure parting to moderate fine granular; soft, very friable, slightly sticky and nonplastic; few very fine roots; few very fine vesicular pores; soil surface has a patchy black cryptogam crust; 10 percent fine gravel and 5 percent small channers; strongly effervescent; moderately alkaline (pH 8.0); clear smooth boundary. (2 to 4 inches thick)
Bk1--2 to 8 inches; light brown (7.5YR 6/4) fine sandy loam, brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; few coarse and medium, many fine and common very fine roots; few very fine continuous tubular pores; 5 percent soft sandstone fragments; 5 percent fine gravel and 5 percent small channers; violently effervescent, secondary calcium carbonates segregated in very few fine irregularly shaped accumulations on undersides of rock fragments; moderately alkaline (pH 8.2); clear smooth boundary. (3 to 10 inches thick)
Bk2--8 to 17 inches; light brown (7.5YR 6/4) fine sandy loam, brown (7.5YR 4/4) moist; weak medium subangular blocky structure; slightly hard, friable, slightly sticky and nonplastic; common coarse and fine and few medium and very fine roots; few very fine continuous tubular pores; 25 percent soft sandstone fragments; 5 percent channers and 5 percent flagstones; violently effervescent, secondary calcium carbonates segregated in few fine irregularly shaped accumulations around rock fragments; moderately alkaline (pH 8.2); clear wavy boundary. (6 to 10 inches thick)
2Bk3--17 to 23 inches; very pale brown (10YR 7/3) loam, light yellowish brown (10YR 6/4) moist; weak very thick platy structure; slightly hard, friable, slightly sticky and nonplastic; few coarse and very fine and common fine roots; few very discontinuous tubular pores; 5 percent soft sandstone fragments; 5 percent channers; violently effervescent, matrix is impregnated with secondary calcium carbonates; moderately alkaline (pH 8.4); clear smooth boundary. (0 to 15 inches thick)
2Bk4--23 to 30 inches; white (10YR 8/1) loam, very pale brown (10YR 7/3) moist; weak thick platy structure; hard, firm, slightly sticky and nonplastic; few coarse to very fine roots; few very fine discontinuous tubular pores; 5 percent soft sandstone fragments; 5 percent channers; violently effervescent, matrix is impregnated and partially cemented in places with secondary calcium carbonates; moderately alkaline (pH 8.4); abrupt smooth boundary. (3 to 11 inches thick)
2R--30 inches; sandstone bedrock.
TYPE LOCATION: San Juan County, New Mexico; on the Navajo Indian Reservation about 16 miles northeast of Shiprock and 0.5 miles south of the Colorado-New Mexico state line; 1,500 feet south and 400 feet east of the northwest corner of sec. 17, T.32N., R.16W.; Latitude 36 degrees 59 minutes 26 seconds N and Longitude 108 degrees 33 minutes 17 seconds W.
RANGE IN CHARACTERISTICS:
Soil moisture - Typically, the soil moisture control section is moist in all parts during the 60 days following the winter solstice. It is moist in some part less than 40 percent of the time and moist in all parts less than 25 percent of the time when the soil temperature at 20 inches is above 41 degrees F. December and August are the wettest months and May and June are the driest.
Mean annual soil temperature - 50 to 52 degrees F.
Depth to lithic contact - 20 to 40 inches to hard sandstone bedrock
Depth to calcic horizon - 2 to 4 inches
Particle-size control section (weighted average):
Silicate clay content - 15 to 18 percent
Rock fragment content - 5 to 15 percent
A horizon
Hue: 7.5YR or 10YR
Value: 5 or 6 dry, 3 to 5 moist
Rock fragments: Total range is 15 to 25 percent 10 to 15 percent fine gravel 5 to 10 percent channers (less than 3 in.)
Calcium carbonate equivalent: 10 to 15 percent
Bk horizons
Hue: 7.5YR or 10YR
Value: 5 through 8 dry, 4 through 7 moist
Chroma: 2 through 4
Texture: fine sandy loam or loam
Rock fragments: Total range is 0 to 15 percent.0 to 5 percent gravel, 0 to 5 channers (less than 3 in.) and 0 to 5 percent flagstones
Calcium carbonate equivalent: 15 to 70 percent
Other features: 0 to 35 percent soft sandstone and 0 to 30 percent soft calcareous siltstone fragments; some pedons have texture of very fine sandy loam or gravelly fine sandy loam.
2Bk horizons (2BCk horizons in some pedons)
Value: 6 through 8 dry, 4 through 7 moist
Chroma: 2 through 4
Texture: fine sandy loam or loam.
Rock fragments: Total range is 0 to 15 percent, 0 to 10 channers (less than 3 in.), 0 to 5 flagstones
Calcium carbonate equivalent: 40 to 90 percent
Other features: 5 to 25 percent soft sandstone and 0 to 40 percent soft calcareous siltstone fragments; some pedons have texture of channery fine sandy loam or flaggy fine sandy loam.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Atlatl soils are on knolls and rims of plateaus and mesas, and on dipslopes of cuestas. They formed in eolian material, alluvium, and residuum derived from calcareous Cretaceous sandstone and siltstone. Slopes are 1 to 15 percent. Elevation ranges from 6,300 to 7,900 feet. The mean annual precipitation is 12 to 16 inches with about half falling as winter snow and half falling as rain from high-intensity convective thunderstorms between July and September. The mean annual temperature is 48 to 50 degrees F. The average frost-free period is 130 to 150 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Vessilla and Wetherill (T) soils. Vessilla soils are shallow to sandstone and occur on structural benches above canyons which dissect the plateaus. Wetherill soils are very deep, fine-silty, and occur on summits of plateaus and dipslopes of cuestas which are mantled with eolian deposits.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; moderate permeability.
USE AND VEGETATION: Atlatl soils are used as a source of fuelwood and for limited livestock grazing. Present vegetation is pinyon and Utah juniper, with an understory of muttongrass, Indian ricegrass, green Mormon tea, thrifty goldenweed, datil yucca, and various forbs.
DISTRIBUTION AND EXTENT: Atlatl soils are of small extent on the Four Corners Platform and Red Rock Bench portions of the Colorado Plateau province in northwest New Mexico, northeast Arizona, and southwest Colorado. MLRA 36.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Shiprock Area, Parts of San Juan County, New Mexico and Apache County, Arizona; 1993.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from the soil surface to a depth of about 2 inches. (A horizon)
Calcic horizon - The zone from 2 to about 30 inches. (Bk1, Bk2, 2Bk3, and 2Bk4 horizons)
Lithic contact - The presence of hard sedimentary bedrock at about 30 inches.
ADDITIONAL DATA: Calcium carbonate equivalence determined on three pedons with a field volume calcimeter.
Classified according to Keys to Soil Taxonomy Ninth Edition, 2003.