LOCATION HILLSBORO OR+WAEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Ultic Argixerolls
TYPICAL PEDON: Hillsboro silt loam, cultivated. (Colors are for moist soil unless otherwise noted.)
Ap1--0 to 4 inches; dark brown (10YR 3/3) loam, brown (10YR 5/3) dry; weak medium and fine subangular blocky structure; slightly hard, friable, nonsticky and nonplastic; many very fine roots; many irregular pores; common fine shot; strongly acid (pH 5.3); abrupt smooth boundary. (4 to 6 inches thick)
Ap2--4 to 11 inches; dark brown (10YR 3/3) loam, brown (10YR 5/3) dry; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and nonplastic; common very fine roots; many irregular pores; common fine shot; strongly acid (pH 5.3); abrupt smooth boundary. (5 to 7 inches thick)
A3--11 to 15 inches; dark brown (10YR 3/3) loam, yellowish brown (10YR 5/4) dry; weak medium prismatic and weak medium subangular blocky structure; slightly hard, friable, slightly sticky and nonplastic; common very fine roots; common very fine tubular pores; medium acid (pH 5.9); clear smooth lower boundary. (0 to 7 inches thick)
B21t--15 to 25 inches; dark brown (10YR 4/3) loam, pale brown (10YR 6/3) dry; weak medium prismatic and weak medium and fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; common very fine and fine tubular pores; few thin clay films on vertical and horizontal faces of peds and in pores; strongly acid (pH 5.5); clear smooth boundary. (8 to 12 inches thick)
B22t--25 to 33 inches; dark brown (10YR 4/3) loam, pale brown (10YR 6/3) dry; weak medium and fine subangular blocky structure; slightly hard, firm, slightly sticky and plastic; few very fine roots; many fine and very fine tubular pores; many moderately thick clay films on vertical and horizontal faces of peds and in pores; strongly acid (pH 5.5); clear smooth boundary. (8 to 11 inches thick)
B3t--33 to 48 inches; dark brown (10YR 4/3) loam, pale brown (10YR 6/3) dry; weak medium subangular blocky structure; slightly hard, firm, slightly sticky and slightly plastic; few very fine roots; many fine and very fine tubular pores; few thin clay films on peds and thick clay films in pores and channels; strongly acid (pH 5.4); clear smooth boundary. (14 to 18 inches thick)
IIC1--48 to 57 inches; dark brown (10YR 4/3) fine sandy loam, massive; soft, friable, nonsticky and nonplastic; few very fine roots; few very fine pores; medium acid (pH 5.6); abrupt smooth boundary. (0 to 10 inches thick)
IIIC2--57 to 63 inches; dark brown (10YR 4/3) loamy fine sand; massive; soft, very friable, nonsticky and nonplastic; medium acid (pH 6.0); abrupt smooth lower boundary. (0 to 6 inches thick)
IVC3--63 to 81 inches; dark brown (10YR 4/3) fine sand; massive; hard, firm, rounded oblong lumps of fine sandy loam arranged horizontally in stratified bands comprise about 15 percent by volume of the horizon; medium acid (pH 5.9).
TYPE LOCATION: Washington County, Oregon; about 1/4 mile east of U. S. 99W on south side of Ore 212; NE corner of section 22, T.2S., R.1W.
RANGE IN CHARACTERISTICS: The soils are usually moist but are dry throughout between depths of 4 and 12 inches for more than 45 consecutive days during the summer. The mean annual soil temperature ranges from 54 to 56 degrees F. The mollic epipedon is 10 to 15 inches thick.
The Ap horizon has hue of 10YR or 7.5YR. It is loam or silt loam.
The Bt horizon is dark yellowish brown (10YR 3/4, 4/4) or dark brown (10YR 4/3) moist and pale brown (10YR 6/3) or light yellowish brown (10YR 6/4) dry. It is loam or silt loam and has 18 to 27 percent clay and less than 15 percent coarser than very fine sand in the upper 20 inches of the Bt horizon. This horizon has dominantly weak subangular blocky structure that ranges to moderate. Clay films are few to many and thin to moderately thick.
Stratified lenses of loamy and sandy material occur below depth of 40 inches.
COMPETING SERIES: These are the Larkin, Latourell, Naff, Van Horn and Willamette series. Larkin soils have moist value of 2 and chroma of 1 or 2 in the upper part of the mollic epipedon, have silty clay loam argillic horizons and have light gray silt coatings on surfaces of peds. Latourell soils have ochric epipedons and have more than 15 percent coarser than very fine sand. Naff soils formed in loess and have very dark brown A horizons and silty clay loam argillic horizons. Van Horn soils have clay loam and sandy clay loam argillic horizons with more than 15 percent coarser than very fine sand. Willamette soils have mollic epipedons thicker than 20 inches.
GEOGRAPHIC SETTING: The Hillsboro soils are on nearly level to gently undulating broad valley terraces with moderate to strongly sloping fronts at elevations of 160 to 240 feet. The soils formed in mixed, silty and loamy old alluvium. The climate is humid temperate with cool moist winters and warm dry summers. The average July temperature is 67 degrees F.; the average January temperature is 39 degrees F.; the average annual temperature is 52 to 54 degrees F. The average annual rainfall is 40 to 50 inches. The frost free period is 165 to 210 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Quatama, Aloha, and Woodburn soils and the competing Willamette soils. Quatama soils are moderately well drained and have ochric epipedons. Aloha soils have mottles within depths of 30 inches and lack argillic horizons. Woodburn soils are moderately well drained, moderately fine textured, and have mottles above depth of 30 inches.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderate permeability.
USE AND VEGETATION: Most areas have been cleared and are used for orchards, berries, nursery stock, vegetables, small grain, hay, and pasture. Native vegetation is Douglas fir, hazelbrush, blackberries, grasses and weeds.
DISTRIBUTION AND EXTENT: Tualatin Valley and northern part of Willamette Valley Oregon and southwestern Washington. The soil is inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Washington County, Oregon, 1919.
ADDITIONAL DATA: Characterization data on two profiles (S59-OR-34-3, 4) reported in Riverside Soil Survey Laboratory Report for Soils from Central Western Oregon, May 1963. Percent clay in the argillic horizon is based on 15 bar water values ranging from about 11 to 13 percent.