LOCATION CLATSOP OR+CA WA

Established Series
Rev. JAS/TDT
02/2011

CLATSOP SERIES

The Clatsop series consists of deep, very poorly drained soils formed in mixed alluvium along tide influenced flood plains. Slopes are 0 to 3 percent. The mean annual temperature is about 51 degrees F. and the mean annual precipitation is about 80 inches.

TAXONOMIC CLASS: Fine-silty, mixed, superactive, nonacid, isomesic Histic Humaquepts

TYPICAL PEDON: Clatsop muck - native vegetation. (Colors are for moist soil unless otherwise noted.)

Oa--0 to 6 inches; very dark grayish brown (2.5Y 3/2) muck, light brownish gray (2.5Y 6/2) dry; weak very fine granular structure; friable; many very fine and fine roots; many very fine irregular pores; slightly acid (pH 6.4); gradual smooth boundary. (5 to 15 inches thick)

A--6 to 13 inches; very dark grayish brown (2.5Y 3/2) mucky silt loam; light brownish gray (2.5Y 6/2) dry; weak fine and very fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine roots; many very fine irregular pores; slightly acid (pH 6.2); clear smooth boundary. (6 to 8 inches thick)

Cg--13 to 24 inches; dark gray (5Y 4/1) silt loam, light brownish gray (2.5Y 6/2) dry; massive; slightly hard, friable, slightly sticky and slightly plastic and slightly fluid; common very fine roots; common very fine tubular pores; slightly acid (pH 6.4); clear smooth boundary. (8 to 11 inches thick)

2Cg--24 to 60 inches; very dark gray (5Y 3/1) silt loam, light brownish gray (2.5Y 6/2) dry; massive; slightly hard, friable, slightly sticky and slightly plastic and very fluid; few very fine roots; few very fine tubular pores; neutral (pH 6.6).

TYPE LOCATION: Clatsop County, Oregon; about 100 feet north of railroad tracks; SE1/4SE1/4SE1/4 section 17, T. 8 N., R. 8 W.

RANGE IN CHARACTERISTICS: The mean annual soil temperature is 47 to 54 degrees F. The difference between the mean summer and mean winter soil temperature varies from 5 to 9 degrees F. The soil is usually saturated throughout and is inundated by high tides unless protected by dikes or levees. Where diked and drained the soil is dry for less than 45 consecutive days in the moisture control section. Depth to massive very dark gray or dark gray 2Cg horizon is less than 30 inches. Under natural conditions, the Oa horizon contains 50 to 70 percent organic matter. Where the Oa horizon is less than 8 inches thick; the Oa and A horizons when mixed to a depth of 10 inches has 15 percent or more organic matter. Under natural conditions soil pH is moderately acid to neutral. When diked and drained soil pH is extremely acid to very strongly acid, but may be strongly acid to moderately acid below 40 inches. In areas that are diked and drained faint to prominent redoximorphic features may occur throughout the profile.

The Oa and A or Ap horizon have hue of 10YR or 2.5Y, value of 3 through 6 and chroma of 1 through 3. The Oa horizon is muck or mucky peat, and has weak granular or weak subangular blocky structure, or is massive. Fiber content ranges from 5 to 45 percent unrubbed, 0 to 20 percent rubbed. The A horizon is mucky silt loam or mucky silty clay loam and has 20 to 35 percent clay. The A horizon has weak subangular blocky structure or is massive.

The Cg horizon has hue of 10YR, 2.5Y or 5Y, value of 3 or 4 and chroma of 1 or less. It is silt loam or silty clay loam with 20 to 35 percent clay and less than 15 percent coarser than very fine sand. This horizon has thin lenses of peat, muck, or sand in some pedons.

The 2Cg horizon has hue of 5Y or neutral, value of 3 or 4, and chroma of 1 or less. It is silt loam or silty clay loam with 20 to 35 percent clay and less than 15 percent coarser than very fine sand. Thin lenses of fine or medium sand occurs in some pedons. Silty clay and clay textures may occur below 40 inches. Buried logs, branches, and fragments of aquatic plants are common in bay sediments.

COMPETING SERIES: There are no other series in this family.

GEOGRAPHIC SETTING: Clatsop soils have formed in depressional areas of tide influenced flood plains along bays and streams that flow into the ocean. The soils formed in recent alluvium over marine bay sediment. They are at elevations of 0 to 10 and are subject to tidal overflow unless protected by dikes or levees. Slopes are 0 to 3 percent. The climate is characterized cool moist summers and cool wet winters. The mean annual precipitation is 50 to 120 inches. Mean July temperature is about 59 degrees F., mean January temperature is about 38 degrees F., mean annual temperature is 45 to 54 degrees F. The frost-free season is 180 to 245 days. The soils are on the Horseshoe geomorphic surface.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Brenner, Brallier, Nehalem, Nestucca and Coquille soils. Brenner, Nehalem, and Nestucca soils have umbric epipedons. Brallier soils are Histosols. Coquille soils have an ochric epipedon.

DRAINAGE AND PERMEABILITY: Very poorly drained; very slow runoff or ponded; slow permeability. Subject to tidal inundation where not protected by dikes or levees.

USE AND VEGETATION: Native vegetation consists of cattails, horsetails, rushes, sedges, skunkcabbage, tufted hairgrass, Oregon gumweed, saltgrass, pickleweed, Douglas aster and seaside plaintain. Where protected from tidal overflow and drained, permanent pasture is the major use. In the unprotected areas, Clatsop soils are important for wetland wildlife habitat.

DISTRIBUTION AND EXTENT: Tide influenced areas of western Oregon and Washington. The series is inextensive.

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

SERIES ESTABLISHED: Astoria Area, Oregon, 1940.

REMARKS: This draft reflects a change in series classification from fine, mixed, acid, isomesic Histic Tropaquepts; and the type location being moved from a protected area to an unprotected area.

Diagnostic features:

Aquic moisture regime - soil is continuously saturated.

Histic epipedon - The upper 10 inches when mixed has 25 percent organic carbon.

National Cooperative Soil Survey
U.S.A.