LOCATION MOLALLA OR
Established Series
Rev. AJG/GLG
06/2011
MOLALLA SERIES
The Molalla series consists of deep, well drained soils that formed in colluvium weathered from tuffs, breccias, and andesite. Molalla soils are on uplands. Slopes are 2 to 30 percent. The mean annual precipitation is about 65 inches and the mean annual temperature is about 50 degrees F.
TAXONOMIC CLASS: Fine-loamy, isotic, mesic Typic Humudepts
TYPICAL PEDON: Molalla cobbly loam, forested. (Colors are for moist soil unless otherwise noted.)
A1--0 to 5 inches; dark reddish brown (5YR 3/2) cobbly loam, reddish gray (5YR 5/2) dry; moderate fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine, fine, and medium roots; many irregular pores; 15 percent gravel and 15 percent cobbles; moderately acid (pH 5.8); clear smooth boundary. (2 to 10 inches thick)
A2--5 to 13 inches; dark reddish brown (5YR 3/3) loam, reddish brown (5YR 4/3) dry; strong fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine roots; many very fine tubular pores; 10 percent gravel; moderately acid (pH 5.6); clear smooth boundary. (5 to 10 inches thick)
BA--13 to 18 inches; dark reddish brown (5YR 3/4) clay loam; reddish brown (5YR 4/4) dry; moderate medium subangular blocky structure; slightly hard, friable, moderately sticky and moderately plastic; common very fine, fine, and medium roots; many very fine tubular pores; 10 percent gravel; moderately acid (pH 5.6); clear smooth boundary. (5 to 10 inches thick)
Bw1--18 to 26 inches; dark reddish brown (5YR 3/4) paragravelly clay loam; reddish brown (5YR 4/4) dry; strong medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; few very fine and fine roots; many very fine tubular pores; 25 percent weathered gravel; strongly acid (pH 5.4); clear smooth boundary. (5 to 12 inches thick)
Bw2--26 to 34 inches; dark reddish brown (5YR 3/3) clay loam; reddish brown (5YR 4/3) dry; strong medium subangular blocky structure; hard, firm, sticky and plastic; few very fine, fine, and medium roots; many very fine tubular pores; 10 percent weathered gravel; strongly acid (pH 5.2); clear smooth boundary. (8 to 12 inches thick)
BC--34 to 44 inches; dark reddish brown (5YR 3/3) paragravelly clay loam; reddish brown (5YR 4/3) dry; moderate medium subangular blocky structure; slightly hard, friable, sticky and plastic; few very fine, fine, and medium roots; many very fine tubular pores; 30 percent weathered fragments; strongly acid (pH 5.2). (8 to 10 inches thick)
Cr--44 inches; weathered tuffaceous rock.
TYPE LOCATION: Clackamas County, Oregon; about 2 miles SE of the North Fork Dam; in the NW1/4NW1/4SE1/4, section 13, T. 4 S., R. 4 E.
RANGE IN CHARACTERISTICS: The soil is usually moist but is dry between depths of 4 and 12 inches for less than 45 consecutive days during the summer months. The mean annual soil temperature is 51 to 53 degrees F. The umbric epipedon is 10 to 20 inches thick. The solum thickness and depth to bedrock is 40 to 60 inches.
The A horizon has hue of 5YR or redder, value of 2 or 3 moist, 3 or 4 dry, and chroma of 2 or 3 moist and dry. It is loam or silt loam. Rock fragments range from 0 to 30 percent cobbles and 5 to 20 percent gravel.
The Bw horizon has hue of 5YR or redder, value of 3 or 4 moist, 4 or 5 dry, and chroma of 3 or 4 moist and dry. It is clay loam or silty clay loam and averages 30 to 35 percent clay. Rock fragments range from 5 to 25 percent very soft weathered paragravel and 0 to 15 percent hard cobbles.
COMPETING SERIES: These are the
Barbourville,
Bohannon,
Cutshin,
Hembre,
Horeb,
Meda,
Preacher,
Stevenson, and
Wadell series. Barbourville and Cutshin soils lack coarse fragments. Bohannon soils are 20 to 40 inches to a paralithic contact. Hembre and Wadell soils have over 15 percent hard rock fragments in the particle-size control section. Horeb and Preacher soils are very strongly acid. Also, Horeb soils have mottles with chroma of 2 through 6 at depths of 24 to 36 inches. Stevenson soils have hue of 7.5YR or 10YR. Meda soils have sola 20 to 30 inches thick.
GEOGRAPHIC SETTING: Molalla soils are on uplands at elevations of 800 to 1800 feet. Slopes are 2 to 30 percent. The soils formed in colluvium weathered from tuffs, breccias and andesite. Summers are warm and dry and winters are cool and wet. The mean annual precipitation is 60 to 75 inches. The mean annual temperature is 48 to 52 degrees F., mean July temperature is about 67 degrees F., and mean January temperature is about 41 degrees F. The frost-free period is 140 to 200 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Alspaugh,
Cottrell,
Klickitat, and McCully soils. Alspaugh and Cottrell soils have a clayey argillic horizon. Klickitat soils are loamy-skeletal and have a lithic contact. McCully soils have more than 35 percent clay in the particle-size control section.
DRAINAGE AND PERMEABILITY: Well drained; slow or medium runoff; moderate permeability.
USE AND VEGETATION: Molalla soils are used for timber production, wildlife habitat, pasture and recreation. Native vegetation is Douglas-fir, western hemlock, red alder, vine maple, salal, brackenfern and western swordfern.
DISTRIBUTION AND EXTENT: Western slopes of the Cascade Mountains in northwestern Oregon; MLRA 3. The series is inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Clackamas County, Oregon, 1982.
REMARKS: Diagnostic horizons and other features;
Umbric epipedon from 1 to 13 inches
Cambic horizon from 13 to 44 inches
National Cooperative Soil Survey
U.S.A.