LOCATION BENHALL ORTentative Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Pachic Ultic Argixerolls
TYPICAL PEDON: Benhall cobbly loam--on a 6 percent slope at an elevation of 4,860 feet--forestland. (Colors are for dry soil unless otherwise noted. The soil was moist throughout when it was described on June 2, 1998.) The soil surface is covered by a one inch layer of undecomposed to slightly decomposed pine needles.
A1--0 to 3 inches; brown (10YR 5/3) cobbly loam, very dark grayish brown (10YR 3/2) moist; moderate medium granular structure; soft, very friable, slightly sticky and slightly plastic; common very fine and common fine roots; common very fine interstitial and common medium tubular pores; 12 percent pebbles and 10 percent cobbles; slightly acid (pH 6.4); clear smooth boundary. (2 to 4 inches thick)
A2--3 to 21 inches; brown (10YR 5/3) very gravelly loam, dark brown (10YR 3/3) moist; weak medium subangular blocky structure parting to strong medium granular; soft, friable, slightly sticky and slightly plastic; few very fine, common fine, common medium, and few coarse roots; common very fine interstitial and common medium tubular pores; 25 percent pebbles and 12 percent cobbles; slightly acid (pH 6.2); clear smooth boundary. (8 to 20 inches thick)
Bt1--21 to 32 inches; light brown (7.5YR 6/3) very cobbly clay loam, brown (7.5YR 4/3) moist; strong medium subangular blocky structure; slightly hard, friable, moderately sticky and moderately plastic; few very fine, common fine, common medium, and few coarse roots; common fine and common medium tubular pores; common faint clay films on faces of peds; 20 percent pebbles, 15 percent cobbles, and 5 percent stones; slightly acid (pH 6.4); clear smooth boundary. (6 to 14 inches thick)
Bt2--32 to 38 inches; light brown (7.5YR 6/3) very cobbly clay loam, brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; few very fine, few fine, and few medium roots; few very fine and few fine tubular pores; common distinct clay films on faces of peds; 20 percent pebbles, 20 percent cobbles, and 5 percent stones; slightly acid (pH 6.4); clear wavy boundary. (0 to 12 inches thick)
Crt--38 to 44 inches; light brown (7.5YR 6/4) weathered basalt, brown (7.5YR 4/4) moist; few distinct clay films on pararock fragments and few seams of illuvial clay lining fractures in the bedrock. (5 to 22 inches thick)
R--44 inches; hard, unweathered basalt.
TYPE LOCATION: Klamath County, Oregon; near the northwest arm of Gerber Reservoir about 300 feet south of the bridge over Benhall Creek; 950 feet south and 1,450 feet east of the northwest corner of section 2, T. 39 S., R. 13 E.; USGS Goodlow Mountain 7.5 minute topographic quadrangle; 42 degrees 13 minutes 17 seconds north latitude and 121 degrees 8 minutes 55 seconds west longitude, NAD 27.
RANGE IN CHARACTERISTICS:
Soil moisture - Usually moist in winter and spring and dry in summer and fall; xeric moisture regime that borders on aridic.
Mean annual soil temperature - 45 to 47 degrees F.
Mean summer soil temperature - 59 to 61 degrees F.
Mollic epipedon thickness - 20 to 30 inches, includes the Bt1 horizon in some pedons.
Argillic horizon thickness - 8 to 26 inches.
Depth to base of argillic horizon - 30 to 40 inches.
Depth to bedrock - 30 to 40 inches to a paralithic contact. The paralithic material below the contact is weathered basalt. Hard, unweathered bedrock is typically within 60 inches.
Particle-size control section - Clay content: 30 to 35 percent; Rock fragments: 35 to 45 percent, mainly cobbles. Lithology of fragments is basalt.
A1 horizon - Hue: 10YR or 7.5YR.
Value: 4 or 5 dry, 2 or 3 moist.
Chroma: 2 or 3, dry or moist.
Clay content: 18 to 24 percent.
Rock fragments: 15 to 35 percent.
Reaction: Slightly acid or neutral.
Organic matter content: 2 to 4 percent.
A2 horizon - Hue: 10YR or 7.5YR.
Value: 4 or 5 dry, 2 or 3 moist.
Chroma: 2 or 3, dry or moist.
Texture: Cobbly loam, very gravelly loam, or very cobbly loam.
Clay content: 20 to 25 percent.
Rock fragments: 20 to 40 percent.
Reaction: Slightly acid or neutral.
Organic matter content: 2 to 4 percent.
Bt1 horizon - Value: 5 or 6 dry, 3 or 4 moist.
Chroma: 3 or 4, dry or moist.
Texture: Cobbly clay loam or very cobbly clay loam.
Clay content: 27 to 32 percent.
Rock fragments: 30 to 45 percent.
Organic matter content: 1 to 3 percent.
Bt2 horizon (when present) - Value: 5 or 6 dry, 3 or 4 moist.
Chroma: 3 or 4, dry or moist.
Texture: Very cobbly clay loam or very cobbly clay.
Clay content: 30 to 42 percent.
Rock fragments: 35 to 50 percent, mainly as cobbles.
Organic matter content: 0.5 to 2 percent.
COMPETING SERIES: These are the Getaway, Greystoke, Jumbo, Moreglade, Pumpkin (T), Sherval, Smarts, and Toncana series.
Getaway soils are deep to lithic contacts. Greystoke and Jumbo soils are deep to paralithic contacts. Moreglade, Pumpkin, Sherval, Smarts, and Toncana soils are very deep.
GEOGRAPHIC SETTING: Benhall soils are on hills and canyons in plateau landscapes. They typically occur on footslope and backslope positions. These soils formed in slope alluvium and residuum derived from basalt and tuff. Slopes are 0 to 40 percent. Elevations range from 4,800 to 5,400 feet. The climate is characterized by cold, wet winters and warm, dry summers. The mean annual precipitation is 18 to 20 inches. The mean annual temperature is 43 to 45 degrees F., mean January temperature is 25 to 28 degrees F., and the mean July temperature is 56 to 60 degrees F. The frost-free period is 50 to 80 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Casebeer, Devaul, Dranket, Mound, Norcross, and Pankeybasin soils. Casebeer and Norcross soils are clayey and shallow to thin duripans over bedrock. Devaul soils are deep to lithic contacts and have mollic horizons less than 20 inches thick. Dranket and Pankeybasin soils are fine and moderately deep to duripans over bedrock. Mound soils are clayey-skeletal and are deep to paralithic contacts.
DRAINAGE AND PERMEABILITY: Well drained; medium or high surface runoff; moderately slow permeability.
USE AND VEGETATION: Benhall soils are used for timber production, wildlife habitat, livestock grazing, and recreation. The native vegetation is a forest canopy of ponderosa pine with an understory of Ross sedge, Idaho fescue, and squawcarpet.
DISTRIBUTION AND EXTENT: South-central Oregon. These soils are not extensive. MLRA 21.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES PROPOSED: Klamath County (Gerber Block of Fremont National Forest Area), Oregon, 1998. The name is from a creek in the area.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from the soil surface to 21 inches (A1 and A2 horizons).
Argillic horizon - The zone from 21 to 38 inches (Bt1 and Bt2 horizons).
Paralithic contact - The boundary at 38 inches to underlying soft, weathered bedrock (Crt layer).
Particle-size control section - The zone from 21 to 38 inches (Bt1 and Bt2 horizons).