LOCATION BORCO IDEstablished Series
TAXONOMIC CLASS: Sandy-skeletal, mixed, frigid Torrifluventic Haploxerolls
TYPICAL PEDON: Borco gravelly loam, in pastureland - on a 1 percent slope at 5,340 feet elevation. (The profile was moist below 44 inches when described on August 11, 1988. Colors are for air-dry soil unless otherwise stated.)
A--0 to 2 inches; grayish brown (10YR 5/2) gravelly loam, very dark grayish brown (10YR 3/2) moist; weak fine granular structure; soft, friable, nonsticky and slightly plastic; many very fine and fine and few medium roots; many very fine and fine irregular pores; 30 percent gravel; strongly effervescent with disseminated lime; slightly alkaline (pH 7.6); abrupt smooth boundary. (2 to 7 inches thick)
Bk1--2 to 5 inches; brown (10YR 5/3) gravelly loam, very dark grayish brown (10YR 3/2) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, nonsticky and slightly plastic; many very fine and fine, and few medium roots; many very fine and fine irregular pores; 30 percent gravel; strongly effervescent with disseminated lime (6 percent calcium carbonate equivalent); few fine rounded soft lime masses; few faint hard lime coatings on undersides of rock fragments; slightly alkaline (pH 7.7); clear wavy boundary.
Bk2--5 to 10 inches; grayish brown (10YR 5/2) gravelly sandy loam, very dark grayish brown (10YR 3/2) moist; moderate fine and medium subangular blocky structure; slightly hard, firm, nonsticky and slightly plastic; many very fine and fine, and few medium roots; many very fine and fine irregular pores; 30 percent gravel; slightly effervescent with disseminated lime (6 percent calcium carbonate equivalent); few fine rounded soft lime masses; few faint hard lime coatings on undersides of rock fragments; slightly alkaline (pH 7.8); clear wavy boundary. (Combined thickness of the Bk horizons is 6 to 14 inches)
2C1--10 to 20 inches; multicolored, dominantly grayish brown (10YR 5/2) extremely gravelly sand, very dark grayish brown (10YR 3/2) moist; few fine distinct masses of iron accumulation; yellowish brown (10YR 5/4) moist; single grain; loose; common very fine and fine roots; many fine and medium irregular pores; 65 percent gravel; moderately alkaline (pH 7.9); clear wavy boundary. (5 to 18 inches thick)
2C2--20 to 26 inches; multicolored, dominantly light brownish gray (10YR 6/2) extremely gravelly sand, dark grayish brown (10YR 4/2) moist; common medium prominent yellowish brown (10YR 5/8) moist; single grain; masses of iron accumulation on coarse fragments; loose; common very fine, and fine and few medium roots; many very fine and fine, irregular pores; 80 percent gravel, 1 percent cobbles; moderately alkaline (pH 7.9); clear wavy boundary. (0 to 15 inches thick)
2C3--26 to 60 inches; multicolored, dominantly grayish brown (10YR 5/2) extremely gravelly loamy coarse sand, dark brown (10YR 3/3) moist; common medium prominent masses of iron accumulation on course fragments; yellowish brown (10YR 5/8) moist; single grain; loose; common very fine and fine and few medium roots; many fine and medium irregular pores; 80 percent gravel; moderately alkaline (pH 7.9).
TYPE LOCATION: Butte County, Idaho; about 1 mile northwest of Arco, Idaho; about 1,400 feet north and 2,080 feet east from the southwest corner of sec. 26, T. 4N., R. 26E. Latitude - 43 degrees, 38 minutes, 32 seconds North; Longitude - 113 degrees, 19 minutes, 39 seconds West.
RANGE IN CHARACTERISTICS:
Mollic epipedon thickness - 10 to 16 inches
Average annual soil temperature - 40 to 44 degrees F.
Depth to relic mottles and sand and gravel - 10 to 20 inches
Particle-size control section
Clay content - 1 to 6 percent
Rock fragment content (average) - 60 to 80 percent
A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 1 or 2 dry or moist
Reaction - slightly or moderately alkaline
Bk horizons
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Rock fragment content - 25 to 45 percent
Texture - GR-L, GR-SL, GRV-L or GRV-SL
Calcium carbonate equivalent - 3 to 10 percent
Reaction - slightly or moderately alkaline
2C horizons
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 2 or 3 dry or moist
Rock fragment content - 60 to 85 percent
Texture - GRX-S or GRX-LCOS
Reaction - slightly or moderately alkaline
COMPETING SERIES: This is the Smout series. Smout soils lack carbonates in the loamy material above the sand and gravel layer.
GEOGRAPHIC SETTING: Borco soils are on stream terraces and flood plains. Slopes range from 0 to 2 percent. Elevation ranges from 5,000 to 6,300 feet. The soil formed in mixed alluvium. The climate is cold and moist in the winter and warm and dry in the summer. The average annual precipitation is 9 to 13 inches. The average annual air temperature is 38 to 42 degrees F. The frost-free period is 50 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arco, Blackfoot, Borah and Mooretown series. Arco soils are on stream terraces, basin floors and flood plains and have fine-silty particle-size control sections. Blackfoot soils are on flood plains and have fine-loamy particle-size control sections. Borah soils are on flood plains and stream terraces and are poorly drained. Mooretown soils are on flood plains and stream terraces and have coarse-loamy particle-size control sections.
DRAINAGE AND PERMEABILITY: Borco soils have been artificially drained by the impoundment or diversion of water. They are now somewhat excessively drained and have slow runoff. Permeability is moderate in the upper part and very rapid in the lower part.
USE AND VEGETATION: Borco soils are used for irrigated cropland, hayland, and pastureland. They are also used for rangeland and homesites. The major crops are alfalfa and wheat. The native vegetation is basin big sagebrush and wheatgrass.
DISTRIBUTION AND EXTENT: East-central Idaho. The series is not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Custer-Lemhi Counties, Idaho, 1999.
REMARKS: The Borco series was originally described as a drained phase of the Borah series. However, because of artificial drainage the soil moisture regime has changed from aquic to aridic resulting in a different classification and a new soil series. Although a Bk horizon is present in the Borco series it does not have enough soft powdery lime to qualify as a calcic horizon.
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from the surface to 10 inches (A, Bk1 and Bk2 horizons)
Particle-size control section - the zone from 10 to 40 inches (2C1 and 2C2 horizons and part of the 2C3 horizon)