LOCATION LETHA ID+OREstablished Series
The Letha series consists of very deep, somewhat poorly drained soils
on low terraces. They formed in alluvium from acid igneous rocks.
Permeability is moderate. Slopes are 0 to about 3 percent. The
average annual precipitation is about 10 inches, and the average annual
air temperature is about 49 degrees F.
TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, calcareous, mesic Aeric Halaquepts
Halaquepts.
TYPICAL PEDON: Letha fine sandy loam - rangeland. (Colors are for dry
soil unless otherwise noted.)
A--0 to 6 inches; light gray (2.5Y 7/2) fine sandy loam, light
olive brown (2.5Y 5/3) moist; moderate very thin platy and weak very
fine granular structure; friable, slightly sticky; many roots; many
very fine and fine pores; slightly effervescent; very strongly alkaline
(pH 9.4); clear smooth boundary. (3 to 8 inches thick)
Bk1--6 to 11 inches; light yellowish brown (2.5Y 6/3) fine sandy
loam, light olive brown (2.5Y 5/3) moist; weak coarse and medium
subangular blocky structure; hard, friable, slightly sticky; common
roots; common very fine pores; strongly effervescent; very strongly
alkaline (pH 9.7); clear smooth boundary. (2 to 7 inches thick)
Bk2--11 to 27 inches; light yellowish brown (2.5Y 6/3) fine sandy
loam, light olive brown (2.5Y 5/3) moist; weak medium subangular blocky
structure; very hard, firm, slightly sticky and slightly plastic;
common roots; few very fine pores; few thin dark grayish brown (10YR
4/2) films on ped faces; strongly effervescent; very strongly alkaline
(pH 10.4); gradual smooth boundary. (10 to 22 inches thick)
Bn--27 to 35 inches; light yellowish brown (2.5Y 6/3) fine sandy
loam, light olive brown (2.5Y 5/3) moist; massive; very hard, very
friable, slightly sticky; common roots; few very fine pores; slightly
effervescent; very strongly alkaline (pH 10.2); abrupt smooth
boundary. (6 to 10 inches thick)
C1--34 to 43 inches; pale yellow (2.5Y 7/3) fine sandy loam, olive
(2.5Y 4/3) and grayish brown (2.5Y 5/2) moist; few medium faint light
olive brown (2.5Y 5/3) and dark grayish brown (10YR 4/2) mottles;
massive; friable, slightly sticky and slightly plastic; few roots; few
very fine pores; slightly effervescent; very strongly alkaline; abrupt
smooth boundary. (3 to 9 inches thick)
2C2--43 to 60 inches; very gravelly coarse sand; single grain;
loose; slightly effervescent in places; strongly alkaline. (several
feet thick)
TYPE LOCATION: Gem County, Idaho; about seven miles west of Emmett;
500 feet north and 60 feet east of the southwest corner of the NW 1/4
section 8, T.6N., R.2W.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 49 to 54 degrees F
Depth to mottles - 20 to 40 inches
Depth to water table - 36 to 48 inches; May through September
Sodium saturation - greater than 50 percent in some part of the upper
20 inches
Texture of control section - SL, FSL
Clay content of control section - 5 to 15 percent
Reaction - moderately to very strongly alkaline
A horizon
Hue- 10YR or 2.5Y
Value- 5 through 7 dry, 3 through 5 moist
Chroma- 2 or 3
COMPETING SERIES: These are the Argenta, Dunphy and Wabuska soils.
Argenta soils have 20 percent or more durinodes in a friable matrix
above a depth of 40 inches. Dunphy soils have weak silica cementation
within 40 inches of the surface. Wabaska soils have average annual
soil temperatures of 54 to 59 degrees F.
GEOGRAPHIC SETTING: Letha soils are on low terraces at elevations of
2,000 to 3,500 feet. Slopes range from 0 to about 3 percent. The
soils formed in moderately coarse textured alluvium derived from coarse
grained acid igneous rocks. The average annual precipitation is 8 to
12 inches, including 1 to 3 feet of snow. Average annual temperature
is 47 to 52 degrees F. Frost-free period is 140 to 160 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Baldock soils
and the Falk and Moulton soils. Falk and Moulton soils are
noncalcareous. These soils are on landscape positions similar to Letha
soils.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; slow runoff;
moderate permeability. A fluctuating water table is at depths of about
36 to 48 inches in summer.
USE AND VEGETATION: Chiefly irrigated pasture or rangeland.
Vegetation in the potential natural plant community is greasewood,
saltgrass, and basin wildrye.
DISTRIBUTION AND EXTENT: Southwestern Idaho and southeastern Oregon.
Moderately extensive.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Gem County, Idaho, 1949.
National Cooperative Soil Survey