LOCATION MOUNTSOLO WAEstablished Series
TAXONOMIC CLASS: Sandy, mixed, mesic Aquic Xerorthents
TYPICAL PEDON: Mountsolo gravelly sand on a 1 percent slope at an elevation of 500 feet. (Colors are for moist soil unless otherwise stated.)
C--0 to 12 inches; dark gray (10YR 4/1) gravelly sand, light gray (10YR 6/1) dry; single grain; loose, nonsticky and nonplastic; 25 percent pebbles; slightly acid (pH 6.4); abrupt smooth boundary. (10 to 18 inches thick)
Cd1--12 to 48 inches; dark gray (10YR 6/1) gravelly loamy sand, light gray (10YR 7/1) dry; massive (compact) hard, very firm, nonsticky and nonplastic; 30 percent pebbles; slightly acid (pH 6.4); diffuse wavy boundary. (40 to 60 inches thick)
Cd2--48 to 60 inches; dark gray (10YR 4/1) very gravelly loamy sand, light gray (10YR 7/1) dry; massive (compact) slightly hard, very firm, nonsticky and nonplastic; 45 percent pebbles; neutral (pH 6.8).
TYPE LOCATION: Cowlitz County, Washington, about 1 mile east of Toutle, 1,200 feet south and 1,450 feet east of the northwest corner section 29, T. 10 N., R. 1 E.
RANGE IN CHARACTERISTICS: These soils are usually moist, but are dry for 45 to 60 consecutive days following summer solstice. The particle-size control section averages 15 to 50 percent volcanic glass and glass aggregates and is 25 to 35 percent coarse fragments. It is moderately acid to neutral throughout.
The C horizon has hue of 10YR or is neutral, value of 3 to 5 moist, 6 or 7 dry, and chroma of 0 to 2 moist or dry. Texture of the surface layer is variable and ranges from gravelly sand to very gravelly sandy loam.
The Cd1 horizon has value of 3 or 4 moist, 6 or 7 dry, and chroma of 0 to 2 moist or dry. It is gravelly sand or gravelly loamy sand.
The Cd2 horizon has value of 4 or 5 moist, 6 or 7 dry, and chroma of 1 or 2 moist or dry. It is very gravelly loamy sand, gravelly loamy sand, or gravelly sand.
COMPETING SERIES: These are the Maxey series. Maxey soils are less than 15 percent volcanic glass and have a zone of carbonate accumulation at 20 to 40 inches.
GEOGRAPHIC SETTING: The Mountsolo soils are on low river terraces and the Toutle River at elevations of 400 to 1,200 feet. Slopes are 0 to 1 percent. Most Mountsolo soils formed in recent volcanic gravelly mudflows from the May 18, 1980 eruption of Mt. St. Helens. These deposits are 5 to 30 feet in depth. The climate is characterized by cool, dry summers and mild, moist winters. Average annual precipitation is 60 to 80 inches. The mean annual temperature is about 50 degrees F. The growing season (28 degrees F) is 200 to 240 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cowlitz and Carrolls soils. Cowlitz soils are somewhat excessively drained gravelly dredge material. Carrolls soils are somewhat poorly drained soils formed in sandy mudflow that averages less than 15 percent coarse fragments.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; slow runoff; moderately slow permeability. A perched water table is from the surface to 1.5 feet from November through April. It has occasional, brief periods of flooding from November through April.
USE AND VEGETATION: Used for wildlife habitat and urban development. These soils had no vegetation when deposited in 1980. Some areas have been vegetated with grass seedings. Natural revegetation by red alder and Scotch-broom is occurring.
DISTRIBUTION AND EXTENT: Cowlitz County, Washington along the north and south forks of the Toutle River. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Cowlitz County, Washington, 1989.
REMARKS: Diagnostic horizons and features recognized in this pedon are a particle-size control section from 10 to 40 inches that is sandy throughout and averages 30 percent pebbles.