The Mounthat series consists of moderately deep, well drained soils that formed in debris flow and ash over vesicular andesite. These soils are on mountains. Slopes range from 5 to 75 percent. The mean annual precipitation is 40 to 60 inches, and the mean annual temperature is 39 to 44 degrees F.

Taxonomic classification: Medial-skeletal, mixed, frigid Pachic Melanoxerands

Mounthat gravelly sandy loam, in an area of Obie-Mounthat complex, 5 to 15 percent slopes, approximately 6 miles west of Burney, 4 miles north from the intersection of Highway 299 and Bunchgrass Road, 80 feet north-northeast of Bunchgrass Road; about 1,200 feet west and 1,900 feet north of the southeast corner of sec. 18, T. 35 N., R. 2 E., Chalk Mountain quadrangle (7.5 minute series):

A1—0 to 4 inches; dark brown (10YR 3/3) gravelly sandy loam, black (10YR 2/1) moist; moderate very fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine, fine, and medium roots; many very fine interstitial pores; 20 percent gravel and 10 percent cobbles; slightly acid (pH 6.5); clear wavy boundary.

A2—4 to 10 inches; brown (10YR 4/3) gravelly sandy loam, very dark brown (10YR 2/2) moist; weak very fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine, fine, and medium roots; many very fine interstitial pores; 20 percent gravel and 10 percent cobbles; slightly acid (pH 6.5); gradual smooth boundary.

A3—10 to 21 inches; dark brown (10YR 4/3) very cobbly sandy loam, very dark brown (10YR 2/2) moist; weak fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine, fine, and medium roots; many very fine interstitial pores; 15 percent gravel and 10 percent cobbles; 15 percent stones and boulders of nonvesicular andesite; slightly acid (pH 6.5); clear wavy boundary.

2Bw—21 to 27 inches; brown (7.5YR 4/4) very cobbly sandy loam, dark brown (7.5YR 3/4) moist; weak very fine subangular blocky structure; soft, very friable, nonsticky and nonplastic; common very fine, fine, and medium roots; many very fine interstitial pores; 10 percent gravel and 25 percent cobbles; 10 percent stones and boulders of nonvesicular andesite; slightly acid (pH 6.5); gradual wavy boundary.

2Cr—27 inches; weathered vesicular andesite with soil filling fractures.

The depth to paralithic contact ranges from 20 to 40 inches. The particle-size control section (from 10 inches to the paralithic contact) ranges from 35 to 60 percent rock fragments, mostly cobbles and gravel. Reaction is slightly acid or moderately acid throughout.

The A1 and A2 horizons have dry color of 10YR 3/3, 4/2, or 4/3 or 7.5YR 4/4. Moist color is 10YR 2/1 or 2/2. The content of organic matter ranges from 15 to 30 percent. The content of rock fragments, mostly gravel or cobbles, ranges from 15 to 30 percent. NaF pH is 10.0 to 11.0. Base saturation by ammonium acetate ranges from 10 to 25 percent.

The A3 horizon has dry color of 10YR 4/3 or 5/4, 7.5YR 4/4, or 5YR 4/4. Moist color is 10YR 2/2 or 7.5YR 3/2. The content of organic matter ranges from 6 to 10 percent. The texture is very cobbly or very gravelly sandy loam. The content of rock fragments, mostly cobbles or gravel, ranges from 35 to 60 percent. NaF pH is 9.0 to 10.0. Base saturation by ammonium acetate ranges from 1 to 12 percent.

The 2Bw horizon has dry color of 10YR 4/3 or 5/4, 7.5YR 4/4, or 5YR 4/4. Moist color is 10YR 4/3 or 7.5YR 3/4 or 4/4. The content of organic matter ranges from 2 to 5 percent. The texture is very cobbly or very gravelly sandy loam. The content of rock fragments, mostly cobbles or gravel, ranges from 35 to 60 percent. NaF pH is 9.0 to 10.0. Base saturation by ammonium acetate ranges from 5 to 15 percent.