Washington Soil Surveys
Washington has 59 USDA soil survey areas covering a wide range of landscapes and soil conditions. The most common soil order is Mollisols — grassland soils with a thick, dark, fertile topsoil rich in organic matter, making up roughly 35% of surveyed soils. Inceptisols — young soils with minimal horizon development but more than Entisols account for another 19%.
In terms of drainage, 77% of Washington soils are classified as well drained. Drainage class affects everything from septic system design to basement feasibility to garden planning. Use the survey area pages below to see drainage details for specific counties, or look up any address for an exact soil profile.
Soil Types
Mollisols
35% of surveyed soils
Fertile grassland soils with thick, dark topsoil. Among the best for agriculture, building, and gardening.
Inceptisols
19% of surveyed soils
Young but developing soils found in mountains and river terraces. Variable properties — check drainage and bedrock depth.
Andisols
18% of surveyed soils
Volcanic ash soils — light, porous, and fertile. Excellent drainage, but low density can complicate foundations.
Aridisols
6% of surveyed soils
Dry-climate soils with low organic matter. Often have caliche layers that make excavation difficult. Low shrink-swell is good for foundations.
Entisols
6% of surveyed soils
Young soils with little development — found on floodplains, dunes, and steep slopes. Properties vary widely by setting.
Spodosols
5% of surveyed soils
Acidic forest soils with a leached layer. Common under conifers. Often have drainage issues from a compacted subsoil layer.
Alfisols
5% of surveyed soils
Moderately weathered forest soils with clay-enriched subsoil. Productive for agriculture, generally good for building and septic.
Histosols
1% of surveyed soils
Organic peat and muck soils formed in wetlands. Very poor for building (compressible) and septic. Often in regulated wetlands.
Ultisols
1% of surveyed soils
Strongly weathered clay soils of the Southeast. Acidic and naturally low in nutrients. Clay subsoil can slow drainage.
Survey Areas
Adams County, WashingtonAsotin County Area, Washington (Asotin and Garfield Counties)Bangor Naval Station, WashingtonBenton County Area, WashingtonCashmere Mountain Area, Washington, Parts of Chelan and Okanogan CountiesChelan County Area, Washington (Parts of Chelan and Kittitas Counties)City of Seattle, WashingtonCity of Tacoma, WashingtonClallam County Area, WashingtonClark County, WashingtonColumbia County Area, WashingtonColville Indian Reservation (Parts of Ferry and Okanogan Counties), WashingtonCowlitz County, WashingtonDouglas County, WashingtonFranklin County, WashingtonGarfield County Area, WashingtonGifford Pinchot National Forest Area, WashingtonGrant County, WashingtonGrays Harbor County Area, Pacific and Wahkiakum Counties, WashingtonHanford Atomic Energy Reservation, WashingtonIsland County, WashingtonJefferson County Area, WashingtonJoint Base Lewis-McChord Area, Washington, Parts of Pierce and Thurston CountiesKing County Area, WashingtonKitsap County Area, WashingtonKittitas County Area, WashingtonKlickitat County Area, WashingtonLewis County Area, WashingtonLincoln County, WashingtonMakah Indian Reservation, WashingtonMason County, WashingtonMount Baker-Snoqualmie National Forest, WashingtonMount Rainier National Park, WashingtonNorth Cascades National Park Complex, WashingtonNorth Ferry Area, WashingtonOkanogan County Area, WashingtonOkanogan National Forest Area, WashingtonOlympic National Forest Area, Washington (Parts of Clallam, Grays Harbor, Jefferson, and Mason Counties)Olympic National Park, WashingtonPend Oreille County Area, WashingtonPierce County Area, WashingtonQuinault Indian Reservation, WashingtonSan Juan County, WashingtonSkagit County Area, WashingtonSkamania County Area, WashingtonSnohomish County Area, WashingtonSnoqualmie Pass Area, Washington (Parts of King and Pierce Counties)Spokane County, WashingtonStevens County, WashingtonThurston County Area, WashingtonUmatilla National Forest, WashingtonWalla Walla County Area, WashingtonWenatchee National Forest, Naches Area, Washington, Parts of Kittitas and Yakima CountiesWhatcom County Area, WashingtonWhitman County, WashingtonYakama Nation Closed Area, Washington, Parts of Klickitat and Yakima CountiesYakima County Area, WashingtonYakima Nation Irrigated Area, Washington, Part of Yakima CountyYakima Training Center, Parts of Kittitas and Yakima Counties, Washington