LOCATION MARPA CA
Established Series
Rev. SEJ/RCH/DJE/CEJ/SBS
09/2021
MARPA SERIES
The Marpa series consists of moderately deep, well drained soils that formed in material weathered from shale, sandstone, schist and other metavolcanic or metasedimentary rocks. Marpa soils are on mountains. Slopes are 5 to 75 percent. The mean annual precipitation is about 45 inches and the mean annual temperature is about 56 degrees F.
TAXONOMIC CLASS: Loamy-skeletal, mixed, active, mesic Ultic Haploxeralfs
TYPICAL PEDON: Marpa gravelly loam--on a north facing slope of 51 percent under black oak, Douglas-fir, California hazel, poison oak, dogwood and canyon live oak at 1,650 feet elevation. (Colors are for dry soil unless otherwise stated. When described on April 13, 1961, the soil was moist throughout.)
Oi--0 to 1 inches; litter and humus from black oak and Douglas-fir.
A--1 to 7 inches; brown (7.5YR 5/2) gravelly loam, dark reddish brown (5YR 3/3) moist; moderate medium granular structure; soft, very friable, nonsticky and nonplastic; common fine and medium, and few coarse roots; many very fine interstitial, and few fine and medium tubular pores; slightly acid (pH 6.1); gradual wavy boundary. (3 to 14 inches thick).
Bt1--7 to 14 inches; brown (7.5YR 5/4) gravelly loam, dark reddish brown (5YR 3/4) moist; weak medium granular structure; soft, friable, slightly sticky and slightly plastic; common fine and medium, and few coarse roots, common very fine interstitial, and few fine and medium tubular pores; common thin discontinuous clay films in pores and bridging sand grains; slightly acid (pH 6.1); gradual wavy boundary. (7 to 12 inches thick).
Bt2--14 to 27 inches; light brown (7.5YR 6/4) very gravelly clay loam, brown (7.5YR 4/4) moist; massive; hard, friable, slightly sticky and slightly plastic; few very fine and medium roots; common very fine interstitial, and few fine and medium tubular pores; common thick discontinuous clay films in pores and on faces of rock fragments; strongly acid (pH 5.4); gradual smooth boundary. (10 to 26 inches thick).
R--27 to 33 inches; fractured hard shale.
TYPE LOCATION: Shasta County, California; about 3/4 mile north of the Mineral School near the north 1/4 corner section 31, T. 34 N., R. 1 W.
RANGE IN CHARACTERISTICS: Solum thickness and depth to bedrock is 20 to 40 inches. The mean annual soil temperature ranges from 54 degrees to 59 degrees F. The soils are usually moist but are dry in the moisture control section most years between mid June or mid July and mid October. Rock fragments consist mostly of cobbles and gravel and make up 15 to 45 percent of the A horizon and 35 to 75 percent of the Bt horizon.
The A horizon is 7.5YR 4/4, 4/6, 5/2, 5/4, 6/2, 6/4, 7/2; 10YR 5/2, 5/3, 5/4, 6/2, 6/3, 6/4, or 6/6. Moist colors are 5YR 3/3, 3/4, 4/3, 4/4; 7.5YR 3/4, 4/2, 4/4; 10YR 3/3, 3/4, 4/3, 4/4. Texture is gravelly loam or very gravelly sandy clay loam with 12 to 25 percent clay. This horizon has weak or moderate granular structure. It is soft to hard and very friable or friable. Reaction is neutral through moderately acid and the base saturation ranges from 35 to 50 percent.
The Bt horizon is 5YR 5/4, 5/6, 6/4 6/8; 7.5YR 4/4, 5/4, 5/6, 6/4; 10YR 4/3, 4/4, 5/4, 5/6, 6/3, 6/4). Moist colors are 5YR 3/4, 4/4, 4/6, 5/4, 5/6; 7.5YR 3/4, 4/4, 4/6, 5/4, 5/6; 10YR 3/3, 3/4, 4/3, 4/4, 5/4. Texture is clay loam or sandy clay loam modified by gravel or cobbles totaling 35 to 60 percent. The Bt has 27 to 35 percent clay and is gravelly, very gravelly or extremely gravelly. This horizon has 4 to 12 percent more clay than the A horizon. Structure is massive or has moderate subangular blocky. It is slightly hard or hard and is slightly acid to strongly acid. Base saturation ranges from 35 to 60 percent by sum of cations.
COMPETING SERIES: These are the
Abegg,
Asabean (T),
Behemotosh (T),
Collayomi,
Gasper (T),
Hollowtree,
Holohan,
Hoosimbim (T),
Pendola (T)
Skalan, and
Whispering series. Abegg, Asabean, Gasper, Holohan, Hoosimbim, Pendola, and Collayomi soils are more than 40 inches deep to bedrock. Behemotosh soils have a Bt horizon with moist value of 5 or 6, moist chroma of 6 or 8, and have loam or sandy clay loam control sections with 18 to 27 percent clay. Skalan soils have mean annual soil temperature of 47 to 51 degrees F. Whispering soils have base saturation of 50 to 75 percent and are strongly influenced by amorphous material and have obsidian fragments. Hollowtree soils are presently not adequately competed.
GEOGRAPHIC SETTING: The Marpa soils are on mountains. Slopes are 5 to 75 percent. The soils formed in material weathered from hard fractured schist or slightly metamorphosed shales and sandstone. Elevations are 1,500 to 5,000 feet. The climate is continental and subhumid with warm dry summers and cold, moist winters. Mean annual precipitation is 30 to 60 inches. Seasonal snowfall ranges from 5 to 25 inches. Mean January temperature is about 38 degrees F; mean July temperature is about 72 degrees F; and mean annual temperature is 47 to 58 degrees F. Frost-free season is 90 to 250 days.
GEOGRAPHICALLY ASSOCIATED SOILS: This is the
Auburn,
Boomer,
Goulding,
Hilt,
Maymen,
Neuns,
Sheetiron,
Sites, and
Kinkel soils. Auburn soils have a cambic horizon interrupted by bedrock, a solum from 10 to 28 inches thick and soil temperatures are thermic. Boomer soils have a fine-loamy control section and a paralithic contact at depths of 40 to 60 inches. Goulding, Maymen, Neuns, and Sheetiron soils lack an argillic horizon. Also, Goulding and Maymen soils are less than 20 inches to hard bedrock. Hilt soils have a fine-loamy control section with less than 35 percent coarse fragments and a paralithic contact at depths of 20 to 40 inches. Sites soils have a clayey control section with base saturation decreasing to less than 35 percent.
DRAINAGE AND PERMEABILITY: Well drained; low to high runoff; moderately slow permeability.
USE AND VEGETATION: Used mostly for timber production. Vegetation is Douglas-fir, black oak, canyon live oak, poison oak, and other shrubs, grasses and forbs.
DISTRIBUTION AND EXTENT: The Marpa soils are in north central California where they are moderately extensive. MLRA is 5 and MLRA 15.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Shasta County, California, 1978.
REMARKS:
ADDITIONAL DATA: Soil data from U.C. Berkeley soil sample No. 61-45-114 dated 4/13/61. A NSSL pedon sampled as Marpa in Del Norte County: S76CA-015-506.
National Cooperative Soil Survey
U.S.A.