LOCATION LA GRANDE OREstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Pachic Haploxerolls
TYPICAL PEDON: La Grande silt loam, cultivated. (Colors
are for moist soil unless otherwise noted.)
Ap--0 to 7 inches; black (10YR 2/1) silt loam, gray
(10YR 5/1) dry; weak fine granular structure; slightly hard,
friable, slightly sticky and slightly plastic; many very
fine roots; many very fine tubular and irregular pores;
moderately alkaline (pH 8.0); abrupt smooth boundary. (6 to
11 inches thick)
A--7 to 14 inches; black (10YR 2/1) silt loam, dark
grayish brown (10YR 4/2) dry; weak medium prismatic and
moderate fine granular structure; slightly hard, friable,
slightly sticky and slightly plastic; many very fine roots;
many very fine tubular pores; mildly alkaline (pH 7.8);
clear smooth boundary. (5 to 12 inches thick)
AB--14 to 21 inches; very dark grayish brown (10YR 3/2)
silt loam, grayish brown (10YR 5/2) dry; weak medium
subangular blocky structure; slightly hard, friable,
slightly sticky and slightly plastic; many very fine roots;
many very fine and common medium tubular pores; few basalt
pebbles 1/2 to 1 inch in diameter; 25 percent krotovinas of
material from above about 3 to 6 inches in diameter; mildly
alkaline (pH 7.8); clear wavy boundary. (7 to 14 inches
thick)
Bw1--21 to 34 inches; dark yellowish brown (10YR 3/4)
silty clay loam, brown (10YR 5/3) dry; many fine distinct
dark grayish brown (10YR 4/2) and strong brown (7.5YR 4/6,
4/8) mottles; moderate and weak fine subangular blocky
structure; slightly hard, friable, sticky and plastic;
common very fine roots; many very fine and common medium
tubular pores; slightly acid (pH 6.2); gradual smooth
boundary. (9 to 15 inches thick)
Bw2--34 to 44 inches; dark yellowish brown (10YR 3/4)
silty clay loam, brown (10YR 5/3) dry; common fine distinct
dark grayish brown (10YR 4/2) and strong brown (7.5YR 4/8)
mottles; moderate and weak medium and fine subangular blocky structure; slightly hard, friable, sticky and plastic;
common very fine roots; many very fine and few medium
tubular pores; neutral (pH 6.6); clear wavy boundary. (8 to
12 inches thick)
2C--44 to 60 inches; multicolored extremely gravelly
loam; massive; hard, firm, slightly sticky and slightly
plastic; many very fine to medium tubular pores; neutral (pH
6.6).
TYPE LOCATION: Union County, Oregon; 575 feet south of the
southeast corner of shop building and 47 feet west of north,
south field road on Union Experiment Station; NW1/4NE1/4
sec. 24, T. 4 S., R. 39 E.
RANGE IN CHARACTERISTICS: The soils are usually moist, but
are dry between depths of 4 and 12 inches for 60 to 80
consecutive days following the summer solstice. The mean
annual soil temperature is 47 to 53 degrees F, and the mean
summer soil temperature is 66 to 70 degrees F. The soil is
saturated with water within 40 inches of the surface for 90
days during the year where not drained. The soil is
noncalcareous and is slightly acid to moderately alkaline.
The particle-size control section is silt loam to silty clay loam
and averages 22 to 35 percent clay and less than 15 percent
coarser than fine sand fragments. The mollic epipedon is 20
to 40 inches thick.
The A horizon has hue of 10YR or 2.5Y, value of 1 or 2
moist, 3 through 5 dry, and chroma of 1.5 or less.
The Bw horizon has hue of 10YR or 2.5Y, value of 4 or 5 dry,
3 or 4 moist, chroma of 2 or 3 moist and dry to a depth of
20 inches or more and 3 or 4 below this depth. Mottles are
prominent or distinct and have chroma of 2 through 8.
The 2C horizon is stratified and ranges from sand to loam
with rock fragments ranging from 0 to 70 percent. Some
pedons lack rock fragments to a depth of 60 inches or more.
COMPETING SERIES: These are the
Athena,
Tucannon and
Wingville series. Athena soils are well drained. Tucannon
soils are well drained and are 20 to 40 inches deep to
bedrock. Wingville soils are somewhat poorly drained, lack
a cambic horizon and are calcareous in the surface.
GEOGRAPHIC SETTING: The La Grande are on alluvial fans and
low stream terraces. Slopes are 0 to 3 percent. Elevations
are 2,200 to 4,000 feet. The soils formed in recent mixed
alluvium weathered mainly from basaltic, granitic, and
argillitic bedrock. The frost-free period is 110 to 160
days. The mean annual precipitation is 11 to 20 inches.
The mean annual temperature is 45 to 51 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Catherine,
Conley,
Hoopal,
Hot Lake,
Phys, and the competing Wingville
soils. Catherine soils are mottled in the mollic epipedon
and are somewhat poorly drained. Conley soils have an E
horizon and a clay argillic horizon. Hoopal soils have a
duripan and are coarse-loamy. Hot Lake soils are
coarse-silty, calcareous, and moderately alkaline or
strongly alkaline. Phys soils are well drained and
loamy-skeletal.
DRAINAGE AND PERMEABILITY: Moderately well drained; slow
runoff; moderate permeability. A seasonal water table
occurs at a depth of 2 to 4 feet.
USE AND VEGETATION: Mostly cultivated for wheat, alfalfa,
green peas, grass seed, and pasture. Few areas are used for
urban development. The natural vegetation is dominantly
giant wildrye, Nebraska sedge and Baltic rush.
DISTRIBUTION AND EXTENT: Valley basins of eastern Oregon.
The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Grande Ronde Valley Area, Union County,
Oregon; 1926.
ADDITIONAL DATA: Partial characterization (chemical) for 2
pedons (S64-OR-31-1) done by Oregon State University (not
published).