LOCATION MIDPEAK                 WA

Established Series
Rev. BJD/TDT
01/2011

MIDPEAK SERIES

The Midpeak series consists of moderately deep, well drained soils formed in residuum and colluvium from volcanic and sedimentary rock with a component of volcanic ash in the upper part. These soils are on shoulders and ridges of mountains. Slopes are 35 to 65 percent. The mean annual precipitation is about 22 inches, and the mean annual temperature is about 43 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, isotic, frigid Vitrandic Haploxerolls

TYPICAL PEDON: Midpeak gravelly ashy sandy loam, on a southwest facing 56 percent slope at 4,750 feet elevation in a Douglas-fir and ponderosa pine forest. (Colors are for dry soil unless otherwise noted. All textures are apparent field textures.)

Oe--0 to 1 inch; moderately decomposed needles and twigs; abrupt smooth boundary. (1 to 2 inches thick)

A1--1 to 7 inches; grayish brown (10YR 5/2) gravelly ashy sandy loam, very dark grayish brown (10YR 3/2) moist, weak fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine and fine, and few medium and coarse roots; common very fine and fine irregular pores; 20 percent gravel and 5 percent cobbles; neutral (pH 6.8); clear wavy boundary.

A2--7 to 16 inches; brown (10YR 5/3) very gravelly ashy sandy loam, very dark grayish brown (10YR 3/2) moist, weak fine and medium subangular blocky structure parting to weak fine granular; soft, very friable, nonsticky and nonplastic; many very fine and fine, and few medium and coarse roots; common very fine and fine irregular pores; 30 percent gravel and 5 percent cobbles; neutral (pH 6.8); clear wavy boundary. (combined A horizon thickness is 7 to 15 inches)

2Bw--16 to 24 inches; pale brown (10YR 6/3) very gravelly sandy loam, brown (10YR 4/3) moist; weak fine subangular blocky structure; soft, very friable, nonsticky and nonplastic; common very fine, fine and medium roots; few fine irregular pores; 40 percent gravel and 5 percent cobbles; neutral (pH 6.8); clear wavy boundary. (8 to 12 inches thick)

2C--24 to 37 inches; brown (7.5YR 5/3) extremely gravelly sandy loam, brown (7.5YR 4/3) moist; massive; soft, very friable; nonsticky and nonplastic; few very fine and fine roots; few very fine irregular pores; 55 percent gravel and 5 percent cobbles; slightly acid (pH 6.4); adrupt irregular boundary.

2R--37 inches; fractured breccia.

TYPE LOCATION: Okanogan County, Washington; about 2 miles north of Mazama, Wa., 1,500 feet east and 2,200 feet north of the southwest corner of section 13, T. 36 N., R. 19 E. (Latitude 48 degrees, 37 minutes, 13 seconds N., Longitude 120 degrees, 25 minutes 8 seconds W NAD 83.)

RANGE IN CHARACTERISTICS: The mean annual soil temperature is 42 to 45 degrees F. These soils are usually moist but are dry in all parts of the moisture control section for 60 to 75 consecutive days following the summer solstice. The mollic epipedon thickness is 7 to 15 inches. Depth to a lithic contact is 20 to 40 inches. The upper 7 to 15 inches has an estimated moist bulk density of 1.00 to 1.20 g/cc, volcanic glass content of 5 to 20 percent, acid-oxalate extractable aluminum plus one-half of the acid-oxalate extractable iron of 0.4 to 1.0 percent, and 15-bar water retention of 5 to 12 percent for air dried samples. The particle-size control section has 40 to 75 percent rock fragments and 5 to 15 percent clay.

The A horizon has hues of 7.5YR or 10YR, values of 4 or 5 dry, and chromas of 2 or 3 dry or moist.

The 2Bw horizon has hues of 7.5YR or 10YR, value of 5 or 6 dry, 3 or 4 moist, and chromas of 2 or 3 dry or moist. It is very gravelly sandy loam or very cobbly sandy loam. It has 30 to 40 percent gravel and 5 to 20 percent cobbles. Reaction is slightly acid to neutral.

The 2C horizon has hues of 5YR, 7.5YR, 10YR, values of 4 to 6 dry, 3 or 4 moist, and chromas of 2 or 3 dry or moist. It is very gravelly sandy loam, very cobbly sandy loam or extremely gravelly sandy loam. It has 30 to 55 percent gravel and 5 to 20 percent cobbles.

COMPETING SERIES: These are the Bearspring, Cassal, Cherrycreek, Eastpine, Longs, Mineral, Peahke, Scoap, Shalrock, Shilling and Yellcreek soils. The Bearspring, Cassal, Scoap, and Yellcreek soils are greater than 40 inches to bedrock. Frint soils have 18 to 25 percent clay. Mineral soils are formed in granite and have coarse sandy loam textures in the 2C horizon. Peahke soils have 18 to 30 percent clay. Shalrock soils lack 5YR and 7.5YR hues in lower substratum. Cherrycreek soils are deep to bedrock. Eastpine soils are dry for 45 to 60 consecutive days and have a surface bulk density of 0.75 to 0.95 g/cc. Longs soils are deep to bedrock. Shilling soils are very deep.

GEOGRAPHIC SETTING: Midpeak soils are on upper backslopes, shoulders and ridges of mountains. Elevations are 2,300 to 4,500 feet. Slopes are 35 to 65 percent. These soils formed in the red colored breccia, tuffs, sandstones and shales of the Ventura member of the Midnight Peak Formation. The climate is characterized by warm, dry summers and cool, moist winters. The mean annual precipitation ranges from 18 to 24 inches. The mean January temperature is 22 to 26 degrees F.; the mean July temperature is 62 to 67 degrees F.; and the mean annual air temperature is 40 to 44 degrees F. The frost-free season is 90 to 120 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Buckrock, Longort, Thout, Veridge, and Yellcreek soils. Buckrock soil are on open shoulders and ridges and are shallow to bedrock. Longort soils are on south facing backslopes and are moderately deep to densic material. Thout soils are on upper backslopes, shoulders and ridges and have a lighter colored surface. Veridge soils are on north facing backslopes and have an andic volcanic ash mantle.

DRAINAGE AND PERMEABILITY: Well drained, very rapid runoff; moderately rapid permeability.

USE AND VEGETATION: Used for timber production, wildlife habitat, watershed, and recreation. Native vegetation is Douglas-fir and ponderosa pine with an understory of pinegrass, mountainlover, shinyleaf spirea, Saskatoon serviceberry, arrowleaf balsamroot, bluebunch wheatgrass and luina.

DISTRIBUTION AND EXTENT: Northcentral Washington. This series is of small extent.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon

SERIES ESTABLISHED: Okanogan National Forest, Okanogan County, Washington, 2005.

REMARKS: Diagnostic horizons and features in this pedon include: Mollic epipedon - 0 to 15 inches (A1 and A2 horizons
Cambic horizon - 15 to 23 inches (2Bw horizon)
Lithic contact - 36 inches
PSCS - zone from 10 to 36 inches (part of A2, 2Bw and 2C horizons)

---

National Cooperative Soil Survey
U.S.A.