LOCATION TALAPUS OREstablished Series
TAXONOMIC CLASS: Medial-skeletal, amorphic Typic Fulvicryands
TYPICAL PEDON: Talapus very gravelly medial silt loam, forested. (Colors are for moist soil unless otherwise noted.)
Oi--0 to 3 inches; partially decomposed needles, twigs, leaves and cones.
A1--3 to 6 inches; black (10YR 2/1) very gravelly medial silt loam, dark grayish brown (10YR 4/2) dry; moderate medium granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine and fine roots; many very fine and fine irregular pores; 30 percent gravel and 10 percent cobbles; strongly acid (pH 5.2); clear wavy boundary.
A2--6 to 16 inches; very dark brown (10YR 2/2) very gravelly medial silt loam, brown (10YR 4/3) dry; moderate very fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine tubular pores; 45 percent gravel and 10 percent cobbles; strongly acid (pH 5.4); clear wavy boundary. (Combined thickness of the A horizon is 7 to 18 inches)
Bw1--16 to 21 inches; dark brown (7.5YR 3/2) very gravelly medial loam, brown (10YR 5/3) dry; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine roots; many very fine tubular pores; 45 percent gravel and 5 percent cobbles; strongly acid (pH 5.4); clear wavy boundary.
Bw2--21 to 26 inches; dark brown (7.5YR 3/3) extremely gravelly medial loam; brown (10YR 5/3) dry; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine roots; many very fine tubular pores; 70 percent gravel and 10 percent cobbles; strongly acid (pH 5.5); gradual wavy boundary. (Combined thickness of the Bw horizon is 9 to 30 inches)
BC--26 to 35 inches; brown (7.5YR 4/4) extremely gravelly medial loam, yellowish brown (10YR 5/4) dry; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; many very fine tubular pores; 70 percent gravel and 10 percent cobbles; strongly acid (pH 5.5); gradual wavy boundary. (10 to 20 inches thick)
2C--35 to 63 inches; dark reddish brown (5YR 3/4) extremely gravelly medial loam, light yellowish brown (10YR 6/4) dry; massive; hard, firm, slightly sticky and slightly plastic; few fine and medium roots; many very fine tubular pores; 70 percent gravel and 10 percent cobbles; strongly acid (pH 5.2).
TYPE LOCATION: Multnomah County, Oregon; Mt. Talapus; SW1/4 NE1/4 SW1/4 section 20, T. 1 N. R. 7 E.
RANGE IN CHARACTERISTICS: The soil is usually moist and are dry for less than 45 consecutive days during the summer months between depths of 8 to 24 inches. The mean annual soil temperature is 40 to 44 degrees F. Depth to bedrock is more than 60 inches. The depth to firm glacial till is 30 to 60 inches. The solum ranges from 24 to 48 inches thick. The particle-size control section has greater than 85 percent phosphate retention, acid oxalate extractable aluminum plus one-half iron of more than 2.0 percent, and 15 to 30 percent 15-bar moisture based on an air-dried sample. The moist bulk density is 0.85 to 0.90 grams per cubic centimeter. Rock fragments range from 35 to 80 percent in the particle size control section. The soils are strongly acid or very strongly acid. Umbric epipedon is more than 20 inches thick.
The A horizon has hue of 10YR or 7.5YR, value of 2 or 3 moist, 3 or 4 dry, and chroma of 1 or 2 moist and 1 through 3 dry. It is very gravelly medial loam or very gravelly medial silt loam with 30 to 45 percent gravel and 5 to 15 percent cobbles. It has moderate or strong granular structure in the upper few inches and strong fine and very fine subangular or blocky structure in the major portion of the A horizon. Organic matter is 10 to 15 percent.
The Bw horizon has hue of 7.5YR or 10YR, value of 3 or 4 moist and 4 or 5 dry, and chroma of 3 or 4 moist and dry. It is extremely gravelly medial loam or extremely gravelly medial silt loam and averages 10 to 18 percent clay. It has 45 to 70 percent gravel and 5 to 15 percent cobbles. Organic matter is 2 to 8 percent.
The 2C horizon has hue of 10YR, 7.5YR or 5YR. It is firm or very firm and some pedons are weakly to strongly cemented below depth of 40 inches. It is very cobbly or extremely cobbly loam.
COMPETING SERIES: This is the Hummington series. Hummington soils are 20 to 40 inches to bedrock.
GEOGRAPHIC SETTING: The Talapus soils are on slightly uneven slopes in glaciated valleys in the Cascade Mountains. Elevations are 3,300 to 4,800 feet. Slopes are 5 to 60 percent. The soils formed in medium textured glacial till and volcanic ash mixed with colluvium weathered mostly from rocks of the Cascade Andesite Formation (olivine basalts and olivine-bearing andesites), although material weathered from the Rhododendron formation (tuffs, breccias and conglomerates) and Columbia River basalt formation are included in some areas. The climate is characterized by cold wet winters and cool moist summers. The mean annual precipitation ranges from 90 to 145 inches, falling as rain in the fall and spring, and snow in the winter. Rainfall amounts are relatively low in the summer. The mean January temperature is about 30 degrees F.; mean July temperature is about 58 degrees F.; and the mean annual temperature is 38 to 42 degrees F. The frost-free period is 10 to 30 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Lastance soils. The Lastance soils have E horizons and spodic horizons.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: Talapus soils are used for producing timber, watershed protection, wildlife, and recreation. Vegetation is western hemlock, noble fir, Douglas fir, blue huckleberry, rhododendron, beargrass and forbs.
DISTRIBUTION AND EXTENT: Cascade Mountains of northwestern Oregon; MLRA 3. The series is of small extent.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Clackamas County, Oregon (Bull Run, Sandy Area), 1976.
REMARKS: This draft reflects a change in classification based on 1998 Keys to Soil Taxonomy.
Diagnostic horizons and features recognized in this pedon:
Umbric epipedon - from 3 to 26 inches (A1, A2, Bw1, and Bw2 horizons)
Cambic horizon - from 26 to 35 inches (BC horizon)
Particle-size control section - from 3 to 43 inches (A1, A2, Bw1, Bw2, and BC horizons and upper 8 inches of C horizon) with a weighted average of 67 percent rock fragments.
Andic properties - from 3 to 63 inches
More investigation is needed to determine whether the zone from 10 to 20 inches has less than 2.0 cmol A1 (1n KCL).