Physiographic features

Physiographic Features
This ecological site occurs mainly on floodplains and drainageways. Parent materials are mixed alluvium with a mantle of volcanic ash and loess.

Landscapes: Valleys and scablands
Landforms: depressions, floodplains, drainageways

Elevation:
Total range = 390 to 1040 m
(1,285 to 3,405 feet)
Central tendency = 560 to 750 m
(1,835 to 2,465 feet)

Slope (percent):
Total range = 0 to 3 percent
Central tendency = 1 to 2 percent

Water Table Depth:
0 to 92 cm; median = 31 cm
(0 to 36 inches; median = 12inches)

Flooding:
Frequency: occasional to frequent
Duration: brief to long

Ponding:
Frequency: None to frequent
Duration: None to long

Aspect: NA

Table 2. Representative physiographic features

Table 3. Representative physiographic features (actual ranges)

Climatic features

Climatic Features

During the spring and summer, a circulation of air around a high-pressure center brings a prevailing westerly and northwesterly flow of comparatively dry, cool and stable air into the region. As the air moves inland, it becomes warmer and drier which results in a dry season beginning in the late spring and reaching a peak in mid-summer. In the fall and winter, a circulation of air around two pressure centers over the ocean brings a prevailing southwesterly and westerly flow of air into the Pacific Northwest. This air from over the ocean is moist and near the temperature of the water. Condensation occurs as the air moves inland over the cooler land and rises along the windward slopes of the mountains or highlands. This results in a wet season beginning in October, reaching a peak in winter, then gradually decreasing in the spring.

The elevation within the LRU varies from approximately 1,000 feet in the lower river valleys to about 4,900 feet on low mountains and foothills. The annual precipitation increases from 9 inches in the valleys to over 38 inches in the higher terrain. Winter season snowfall averages about 43 inches. Both rainfall and snowfall increase with elevation. Snow can be expected after the first of November and to remain on the ground from the first of December until March or April.

In January, the average maximum temperature is near 29° F and the minimum temperature is 14° F. Minimum temperatures from -5° to -20°F are recorded almost every winter and temperatures ranging to -25° F have been recorded. In July, the average maximum temperature is 81° and the minimum temperature 47° F. Maximum temperatures reach 100° F on a few afternoons each summer and temperatures as high as 108° F have been recorded. The average date of the last freezing temperatures can be expected by early-June and after early-September in the warmer areas.
(Compiled from WRCC: Climate of Washington and available station data)

Frost-free period (days):
Total range = 100 to 140 days
Central tendency = 115 to 125 days

Mean annual precipitation (cm):
Total range = 360 to 855 mm
(14 to 34 inches)
Central tendency = 455 to 615 mm
(18 to 24 inches)

MAAT (C)
Total range = 5.8 to 9.9
(42 to 50 F)
Central tendency = 7.6 to 8.7
(46 to 48 F)

Climate stations: none

Influencing water features

Water Table Depth:
0 to 92 cm; median = 31 cm
(0 to 36 inches; median = 12inches)

Flooding:
Frequency: occasional to frequent
Duration: brief to long

Ponding:
Frequency: None to frequent
Duration: None to long

Soil features

Representative Soil Features
This ecological site is associated with the Cocolalla, Konner, Peone, and Wethey components. The soils are Aquandic Endoaquepts, Aquandic Endoaquolls, Aquic Xerofluvents, Cumulic Endoaquolls. These soils have developed in mixed alluvium. Most sites have a surface influenced by volcanic ash and loess. Volcanic ash layers are mixed at lower elevations and form distinct, moderately thick layers at higher elevations.

Parent Materials:
Kind: volcanic ash, loess
Origin: mixed
Kind: alluvium
Origin: mixed

Surface Texture: (<2mm fraction)
(1) Ashy-Silt Loam
(2) Silty Clay Loam
(3) Loamy Sand

Surface Fragments

Table 4. Representative soil features

Table 5. Representative soil features (actual values)

References

• . USNVC [United States National Vegetation Classification]. 2019. United States National Vegetation Classification Database, V2.03. Federal Geographic Data Committee, Vegetation Subcommittee, Washington DC.. USNVC: http://usnvc.org/.

• Gerald, R. 2004. NRCS - Washington; Interim Ecological Site Descriptions for Rangeland.

• Kovalchik, B.L. and R.R. Clausnitzer. 2004. Classification and Management of Aquatic, Riparian, and Wetland Sites on the National Forests of Eastern Washington: Series Description. General Technical Report PNW-GTR-593. United States Department of Agriculture, Forest Service, Pacific Northwest Research Station. 1–354.

• Rocchio, J.F. and R.C. Crawford. 2015. Ecological systems of Washington State. A guide to identification. Washington Department of Natural Resources.. Natural Heritage Report.. Washington Department of Natural Resources, Natural Heritage Program, Olympia, WA. 1–397.

Contributors

Stephanie Shoemaker
Brian Gardner