LOCATION AVAL OREstablished Series
TAXONOMIC CLASS: Ashy, glassy, frigid Lithic Xeric Haplocambids
TYPICAL PEDON: Aval very gravelly coarse sandy loam-rangeland, on a 5 percent southwest-facing slope at 4,220 feet elevation. (Colors are for dry soil unless otherwise stated.)
A--0 to 2 inches; dark grayish brown (10YR 4/2) very gravelly coarse sandy loam, very dark brown (10YR 2/2) moist; moderate very fine and fine granular structure parting to single grained; loose, nonsticky and nonplastic; few very fine roots; 35 percent gravel; neutral (pH 6.6); abrupt smooth boundary. (1 to 4 inches thick)
Bw1--2 to 7 inches; grayish brown (10YR 5/2) gravelly sandy loam, very dark grayish brown (10YR 3/2) moist; moderate coarse and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine, few fine and medium roots; common very fine tubular pores; 25 percent gravel; slightly alkaline (pH 7.6); clear smooth boundary.
Bw2--7 to 18 inches; brown (10YR 5/3) gravelly coarse sandy loam, very dark grayish brown (10YR 3/2) moist; weak fine and medium subangular blocky structure; soft, very friable, nonsticky and slightly plastic; common very fine, and few fine, medium and coarse roots; common very fine tubular pores; 30 percent gravel and 2 percent cobbles; slightly alkaline (pH 7.7); abrupt wavy boundary. (Combined thickness of the Bw horizon is 9 to 16 inches thick)
2R--18 inches; welded tuff.
TYPE LOCATION: Harney County, Oregon, in Diamond Craters Research Natural Area, about 2,200 feet north and 1,400 feet west of the southeast corner of section 15, T. 29 S., R. 32 E. (Latitude 43 degrees 2 minutes 30 seconds W, Longitude 118 degrees 44 minutes 38 seconds W)
RANGE IN CHARACTERISTICS: The mean annual soil temperature is 45 to 47 degrees F. The soil moisture control section is dry for one-half to three-fourths of the time the soil temperature is above 41 degrees F. The mollic colors in the Bw horizon are from the parent material. The thickness of the solum and depth to hard bedrock is 10 to 20 inches. The particle size control section averages 15 to 35 percent rock fragments mainly as gravel size cinders and 5 to 18 percent clay. A weathered bedrock layer overlies hard bedrock in some pedons. It contains 40 to 85 percent volcanic glass in the 0.02 to 0.25 mm size fraction. Phosphate retention is 15 to 25 percent. The acid oxalate aluminum plus one-half the iron is 0.5 to 1.0 percent.
The A horizon has values of 4 or 5 dry, 2 or 3 moist, and chroma of 2 or 3. It has 1 to 3 percent organic matter. It has 35 to 50 percent gravel size cinders.
The Bw horizon is gravelly sandy loam, gravelly loam, or gravelly coarse sandy loam. Rock fragment content is 15 to 35 percent cinders. Clay content is 5 to 18 percent. It has 0.5 to 1.0 percent organic matter.
COMPETING SERIES: This is the Arron (T) series. The Arron soils are dominated by light colored pumice sand from Mt. Mazama, the rock fragments are basalt or tuff.
GEOGRAPHIC SETTING: Aval soils are on hills near volcanic vents and have slopes of 2 to 20 percent. The soils formed in cinders and eolian deposits over welded tuff and basalt. Elevations are 4,100 to 4,700 feet. The climate is characterized cold, moist winters and hot, dry summers. The mean annual precipitation is 10 to 12 inches. The mean annual temperature is 43 to 35 degrees F. The frost free period is 50 to 80 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Flank, Pomerening, Srednic soils. Flank soils have greater than 35 percent coarse fragments. Pomerening soils are very deep. Srednic soils are moderately deep over a duripan.
DRAINAGE AND PERMEABILITY: Well drained, permeability is moderately rapid.
USE AND VEGETATION: The soils are used for recreation and wildlife. Potential native vegetation is basin big sage, needleandthread, and Thurbers needlegrass.
DISTRIBUTION AND EXTENT: Holocene age volcanic areas of southeast Oregon; MLRA 23. Series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Harney County, Oregon, 1997.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the dark colors are from the parent material.
Cambic horizon - from 2 to 18 inches (Bw1, Bw2 horizons).
Particle-size control section - from 10 to 18 inches (Bw2 horizon).
For organic carbon and andic soil properties analysis, see data for the associated Srednic series, pedon S93OR-025-002