LOCATION DARBY OR
Established Series
Rev. ACT/TDT
01/2023
DARBY SERIES
The Darby series consists of deep, well drained soils that formed in colluvium weathered from basalt of the Roseburg Formation. Darby soils are on mountainsides, fans and foot slopes and have slopes of 12 to 60 percent. The mean annual precipitation is about 45 inches and the mean annual temperature is about 52 degrees F.
TAXONOMIC CLASS: Fine, mixed, superactive, mesic Pachic Ultic Argixerolls
TYPICAL PEDON: Darby silt loam-forested. (Colors are for moist soil unless otherwise noted.)
Oi--1 inch to 0; fern leaves, Douglas-fir needles, twigs.
A--0 to 5 inches; very dark brown (7.5YR 2/2) silty clay loam, dark grayish brown (10YR 4/2) dry; moderate fine subangular blocky structure; hard, friable, sticky and plastic; common very fine to medium roots; many very fine to medium irregular pores; neutral (pH 7.0); abrupt smooth boundary. (4 to 8 inches thick)
BA--5 to 10 inches; very dark brown (7.5YR 2/2) silty clay loam, dark grayish brown (10YR 4/2) dry; moderate fine subangular blocky structure; hard, friable, sticky and plastic; common very fine to medium roots; many very fine irregular and few fine tubular pores; slightly acid (pH 6.4); clear wavy boundary. (0 to 8 inches thick)
Bt1--10 to 19 inches; very dark brown (7.5YR 2/2) silty clay, dark brown (10YR 3/3) dry; strong medium angular and subangular blocky structure; very hard, firm, very sticky and very plastic; common fine and medium roots; many very fine irregular and few fine tubular pores; common faint clay films on faces of peds; neutral (pH 6.8); clear wavy boundary. (8 to 15 inches thick)
Bt2--19 to 30 inches; very dark brown (7.5YR 2/2) silty clay, dark brown (10YR 3/3) dry; strong medium angular and subangular blocky structure; extremely hard, firm, very sticky and very plastic; few fine and very fine roots; many very fine and fine irregular pores; many distinct clay films on faces of peds; neutral (pH 6.8); clear wavy boundary. (10 to 25 inches thick)
Bt3--30 to 44 inches; very dark brown (10YR 2/2) silty clay, dark brown (10YR 3/3) dry; dark yellowish brown (10YR 3/4) dry crushed; strong angular blocky structure; very hard, firm, very sticky and very plastic; common fine and medium roots; many very fine irregular pores; many prominent clay skins on faces of peds; 15 percent fine gravel; neutral (pH 6.8); clear smooth boundary. (5 to 15 inches thick)
BCt--44 to 61 inches; dark yellowish brown (10YR 4/4) silty clay loam, yellowish brown (10YR 5/4) dry; moderate medium subangular blocky structure; hard, firm, sticky and plastic; few very fine roots; many very fine pores; few distinct clay films on faces of peds; 15 percent gravel; neutral (pH 6.8); clear smooth boundary (6 to 20 inches thick)
Cr--61 inches; weathered basalt.
TYPE LOCATION: Douglas County, Oregon; about 2.5 miles south of the community of Nonpareil; 2,300 feet north and 450 feet west of the SE corner of section 27, T. 25 S., R. 4 W.
RANGE IN CHARACTERISTICS: The mean annual soil temperature ranges from 52 to 57 degrees F. The moisture control section is dry for 45 to 60 consecutive days after the summer solstice. Depth to bedrock commonly is 60 to 80 inches but it is as shallow as 45 to 60 inches in some pedons. Hue is from 10YR or 7.5YR. The mollic epipedon is 30 to 60 inches thick.
The A horizon has value of 2 or 3 moist, 3 or 4 dry and chroma of 1 through 3 moist and dry. Coarse fragments range from 0 to 10 percent gravel and cobbles.
The Bt horizon has value of 2 or 3 moist and 3 or 4 dry in the upper part and 2 through 4 moist and 3 through 5 dry in the lower part, and chroma of 1 through 3 moist and dry. This horizon is clay or silty clay, averaging 40 to 50 percent clay with 5 to 15 percent gravel and cobbles.
The BCt or C horizon is clay loam, loam, or silty clay loam with 5 to 15 percent gravel and cobbles.
COMPETING SERIES: These are the
Coburg,
Dixonville,
Malabon,
Mart,
Redbell and
Silverton series. Coburg soils have redoximorphic features at a depth of 20 to 36 inches. Dixonville soils have a paralithic contact at a depth of 20 to 40 inches. Malabon soils have a mollic epipedon 20 to 30 inches thick. Mart soils have a mean annual soil temperature of 48 to 52 degrees F. Redbell soils are dry for 60 to 80 consecutive days and have redoximorphic features within 30 inches of the surface. Silverton soils are 25 to 40 inches deep to a lithic contact.
GEOGRAPHIC SETTING: Darby soils are on foot slopes, fans and mountainsides in mountainous uplands. Slopes are 12 to 60 percent. Elevations are 400 to 2,600 feet. The soils formed in colluvium and residuum weathered from basalt of the Roseburg Formation. The climate is characterized by cool moist winters and dry warm summers. The mean annual precipitation is 30 to 60 inches. Mean January temperature is 39 degrees F.; mean July temperature is 60 degrees F.; the average annual temperature is 50 to 55 degrees F. The frost-free season is about 160 to 235 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Jory,
Nekia,
Philomath and
Ritner soils and the competing
Dixonville soils. Nekia soils lack a mollic epipedon. Ritner soils lack an argillic horizon. Philomath soils lack an argillic horizon and are less than 20 inches deep to a paralithic contact.
DRAINAGE AND PERMEABILITY: Well drained; slow to rapid runoff; slow permeability.
USE AND VEGETATION: Timber production, pasture, hay, homesites, wildlife habitat, and watershed. Native vegetation is dominantly Oregon white oak, California black oak, Douglas fir, grasses, and poison oak.
DISTRIBUTION AND EXTENT: Footslopes of the Coast Range and Cascade Mountains in western Oregon. MLRA 2. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Douglas County, Oregon, 1995.
REMARKS: The superactive cation exchange activity class was added to the classification in 10/2005. The competing series section was not updated at that time. Last revision 3/1995.
National Cooperative Soil Survey
U.S.A.