LOCATION MILLSAP                 CA

Established Series


The Millsap series consists of moderately deep, well drained soils that formed in material weathered from hard sandstone and shale. Millsap soils are on hillslopes in the Coast Range foothills and have slopes of 5 to 75 percent. The mean annual precipitation is 24 inches and mean annual temperature is about 60 degrees F.

TAXONOMIC CLASS: Fine, mixed, superactive, thermic Typic Palexeralfs

TYPICAL PEDON: Millsap loam, on a south-facing slope of 35 percent under grasses, forbs, and scattered oak at 1,400 feet elevation. (Colors are for dry soil unless otherwise stated.)

A--0 to 2 inches; grayish brown (10YR 5/2) loam, very dark grayish brown (10YR 3/2) moist; moderate medium platy structure; hard, friable, nonsticky and nonplastic; many fine roots; many fine pores; 7 percent gravel; slightly acid; abrupt wavy boundary. (0 to 3 inches thick)

AB--2 to 9 inches; brown (10YR 5/3) clay loam, brown (10YR 4/3) moist; moderate medium subangular blocky structure; hard, firm, slightly sticky and slightly plastic; many fine roots; many fine pores; thin patchy clay films in pores; 5 percent gravel; slightly acid; abrupt irregular boundary. (5 to 12 inches thick)

Bt1--9 to 31 inches; brown (10YR 5/3) clay, brown (10YR 4/3) moist; strong very coarse prismatic structure; extremely hard, very firm, very sticky and very plastic; few fine roots; many fine pores; continuous clay films in pores and on peds; 10 percent gravel, mostly in lower part; slightly acid; irregular boundary. (15 to 25 inches thick)

Bt2--31 to 39 inches; brown (10YR 5/3) extremely gravelly clay, brown (10YR 4/3) moist; strong very coarse prismatic structure; extremely hard, very firm, very sticky and very plastic; few fine roots; many fine pores; continuous clay films in pores and on peds; 63 percent gravel; slightly acid; wavy clear boundary. (0 to 20 inches thick)

R--39 to 45 inches; hard, fractured, partly weathered fine grained sandstone.

TYPE LOCATION: Tehama County, California; 1.5 miles east of Cold Fork; 1/2 mile SW on Pettyjohn Road from Cobb Flat and about 200 feet NW and uphill from the road, in the SW1/4 of the NW1/4 sec. 27, T.27N., R.7W.

RANGE IN CHARACTERISTICS: Depth to a lithic contact ranges from 20 to 40 inches. Mean annual soil temperature is 62 degrees to 66 degrees F. and the soil temperature is not less than 41 degrees F. at any time. The soil between the depths of about 5 and 15 inches is usually dry in all parts from mid-May until mid-October and is moist in some or all parts between these depths all the rest of the year. Most pedons have less than 10 percent rock fragments in all horizons and the entire Bt horizon or the upper 20 inches always averages less than 35 percent. Some pedons have as much as 75 percent rock fragments in the subhorizon just above the bedrock. The base saturation is 80 to 100 percent throughout the soil.

The A horizon is grayish brown, brown, light brownish gray, pale brown, or light yellowish brown (10YR 5/2, 5/3, 6/2, 6/3, 6/4; 2.5Y 5/2, 6/2, 6/4). Moist colors are very dark grayish brown, dark brown, brown or dark yellowish brown (10YR 3/2, 3/3, 3/4, 4/2, 4/3, 4/4, 5/3; 2.5Y 3/2, 4/2). Organic matter averages 0.5 to 4 percent in the upper few inches of the A horizon and decreases abruptly with depth. The dark colors have too little organic matter or are too thin to qualify for a mollic epipedon. This horizon is loam or clay loam and is slightly acid to strongly acid. Some pedons have thin cappings of uncoated grains on top of the Bt horizon or have an E horizon.

The Bt horizon is dark brown, grayish brown, brown, yellowish brown, light brown, or light yellowish brown (10YR 4/3, 5/2, 5/3, 5/4, 6/4; 7.5YR 4/4, 5/4, 6/4). Moist colors are dark brown or dark yellowish brown (10YR 3/3, 3/4, 4/3, 4/4; 7.5YR 4/4). This horizon is heavy clay loam, silty clay, clay, gravelly clay, very gravelly clay or extremely gravelly clay with 15 to 30 percent (absolute) increase in clay from the A horizon to the Bt horizon. It is neutral to moderately acid. Some pedons have BC, BCt, or C horizon without rock structure above the bedrock.

COMPETING SERIES: These are the Cometa and Corning series in the same family and the Hillgate and San Ysidro series. None of these soils have a lithic or paralithic contact. Also, the mineralogy of Hillgate and San Ysidro soils is dominated by montmorillonite.

GEOGRAPHIC SETTING: Millsap soils are on toe slopes and mountains. Slopes are 5 to 75 percent. The soils formed in material weathered from firm to hard sandstone, shale and conglomerate. Elevations are 75 to 3,000 feet. The climate is subhumid with warm to hot dry summers and cool moist winters. Mean annual precipitation is 16 to 30 inches. Mean January temperature is about 42 degrees F.; mean July temperature is about 74 degrees F.; mean annual temperature is about 59 degrees to 62 degrees F. Frost-free season is about 200 to 300 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing San Ysidro soils and the Gaviota, Lodo, Los Osos, Millsholm, Newville, and Sehorn soils. Gaviota, Lodo, and Millsholm soils are less than 20 inches deep to rock and lack an argillic horizon. Los Osos soils have a mollic epipedon, and lack an abrupt A/Bt horizon boundary. Sehorn soils have cracks that open to the surface, have slickensides, and lack an argillic horizon. Newville soils lack a lithic contact, have a moist value of less than 3.5, have more than 1.5 percent organic matter to a depth of more than 4 inches, and have montmorillonitic mineralogy.

DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; very slow permeability.

USE AND VEGETATION: Used mostly for grazing. Vegetation is annual grasses, forbs, and scattered oaks and digger pine. The oaks are mostly blue oak.

DISTRIBUTION AND EXTENT: East side of the Coast Ranges of northern and central California. The soils are moderately extensive.


SERIES ESTABLISHED: Glenn County, California, 1957. The original type location in Glenn County had vermiculitic mineralogy but is only 1,429 acres. As mapped in Glenn County, depths to bedrock ranged from 15 to 30 inches. The present type location and areas subsequently mapped have mixed mineralogy, and depth to bedrock of 20 to 40 inches.

REMARKS: The activity class was added to the classification in February of 2003. Competing series were not checked at that time. - ET
Edits were made to incorporate lab data from the CA645 manuscript as part of the SDJR initiative. - AEC
Millsap where mapped in CA095 Solano County CA and CA664 San Louis Obispo County need to be compared with the central concept of where Millsap is mapped in the northern Coast Range foothills. In CA095 Millsap is moderately well drained and occurs on low hills. In CA664 Millsap occurs on hills and mountains influenced by the marine climate. - AEC

National Cooperative Soil Survey