LOCATION ROCKSTOP ORTentative Series
TAXONOMIC CLASS: Loamy, mixed, superactive, frigid Lithic Xeric Haplargids
TYPICAL PEDON: Rockstop gravelly ashy loam at an elevation of 1,459 meters, rangeland. (Colors are for dry soil unless otherwise noted.) The soil surface is partly covered by 10 percent fine gravel, 10 percent gravel, 10 percent cobbles, and 5 percent stones.
A--0 to 13 cm; light brownish gray (10YR 6/2) gravelly ashy loam, dark grayish brown (10YR 4/2) moist; weak thin platy structure; slightly hard, friable, nonsticky, nonplastic; common fine and very fine roots; many vesicular pores; 10 percent fine gravel, 10 percent gravel, 5 percent cobbles and 1 percent stones; slightly alkaline (pH 7.4); clear wavy boundary. (5 to 13 cm thick)
Bt1--13 to 30 cm; light brownish gray (10YR 6/2) ashy loam, dark brown (10YR 3/3) moist; moderate medium and fine subangular blocky structure; slightly hard, friable, nonsticky, nonplastic; common fine and very fine roots; 2 percent prominent clay films on all faces of peds; 7 percent fine gravel, 2 percent gravel and 2 percent cobbles; slightly alkaline (pH 7.4); clear wavy boundary. (11 to 27 cm thick)
Bt2--30 to 36 cm; yellowish brown (10YR 5/4) ashy loam, brown (10YR 4/3) moist; moderate medium and fine subangular blocky structure; slightly hard, friable, slightly sticky, slightly plastic; 5 percent prominent clay films on all faces of peds; 7 percent fine gravel and 2 percent gravel and 2 percent cobbles; slightly alkaline (pH 7.4); abrupt wavy boundary. (6 to 26 cm thick)
R--36 cm; indurated rhyolite.
TYPE LOCATION: Malheur County, Oregon; approximately 7 miles north west of Jordan Valley, OR; UTM 481322 easting, 4766654 northing, zone 11, NAD83 on the USGS Downey Canyon 7.5 minute quadrangle, latitude 43 degrees 3 minutes 8.00 seconds north and longitude 117 degrees 13 minutes 46.00 seconds west, NAD83.
RANGE IN CHARACTERISTICS:
Soil moisture - The soil moisture control section is dry throughout in summer and fall and moist in winter and spring; the soil surface is wet in April due to snowmelt; aridic moisture regime that borders on xeric.
Soil temperature - The mean annual soil temperature is 7 to 8 degrees C.
Depth to lithic contact - 36 to 50 cm.
Control section - Clay content - 25 to 35 percent.
Rock fragments - 10 to 25 percent, mainly gravel and cobbles with basalt, rhyolite or tuff lithology.
A horizon -
Value: 5 or 6 dry, 3 or 4 moist.
Chroma: 2 or 3 moist.
Reaction: Neutral through slightly alkaline.
Volcanic glass: Volcanic glass is estimated to range from 30 to 50 percent of the 0.2 to 2 mm fraction.
Bt horizons -
Value: 5 or 6 dry, 3 to 5 moist.
Chroma: 2 to 4 dry and moist.
Texture: Ashy loam, ashy clay loam, ashy silty clay loam.
Percent clay: 24 to 35
Rock fragments: 10 to 25 percent gravel and cobbles.
Volcanic glass: Volcanic glass is estimated to range from 5 to 30 percent of the 0.2 to 2 mm fraction.
COMPETING SERIES: These are the Coztur and Punchbowl soils. Coztur soils do not have 30 to 50 percent volcanic glass in the upper part. Punchbowl soils are 20 to 36 cm deep over lithic contacts.
GEOGRAPHIC SETTING: Rockstop soils are on lava plateaus. These soils formed in mixed volcanic ash and loess over residuum weathered from rhyolite and basalt. Slopes are 2 to 15 percent. Elevations are 1,457 to 1,487 meters. The climate is semiarid with cold, moist winters and warm, dry summers. The mean annual precipitation is 280 to 330 mm; mean annual temperature is 5 to 7 degrees C, and the frost-free period is 50 to 80 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Littlegrass and Cowlake soils. The Littlegrass soils are greater than 100 cm to paralithic contact and the Cowlake series has greater than 35 percent rock fragments in the particle-size control section.
DRAINAGE AND PERMEABILITY: Moderately well drained, saturated in the upper part for two weeks or more in spring due to snowmelt, very high runoff, moderate and moderately slow permeability and moderately high saturated hydraulic conductivity,.
USE AND VEGETATION: Rangeland and wildlife habitat. The present vegetation is low sagebrush, Idaho fescue, and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: Southeast Oregon; the soil is of small extent. MLRA 25.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES PROPOSED: Malheur County, Oregon, Southern Part, 2008.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from the soil surface to 13 cm (A horizon).
Argillic horizon - The zone from about 13 to 36 cm (Bt1 and Bt2 horizons).
Ashy textures - Volcanic glass is 30 to 50 percent of the 0.2 to 2 mm fraction in the zone from 0 to 13 cm (A horizon) and 5 to 30 percent in the zone from 13 to 36 cm (Bt1 and Bt2 horizons).
Particle-size control section - The zone from 13 to 36 cm (Bt1 and Bt2 horizons).