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Asotin County, Washington
Shrink-swell clay limits houses without basements on 29% of Asotin County's mapped land, a higher share than 80% of US counties and the highest of 39 Washington counties. A shallow water table limits basements on 5%.
The soil survey maps 82% of the county's land area; these shares describe the mapped part. 100% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 1 flood losses here since 2016. 57% of homes were built before 1980, against 50% nationally; the median home dates from 1976.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Asotin County
| Expansive clay (limits slab homes) | 29.4% |
| High water table (limits basements) | 4.8% |
| Septic fields very limited | 96.8% |
| Clay swell (LEP, by area) | 4.3% |
| High-swell land (LEP 6%+) | 29.9% |
| Mapped soil | 335,161 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Gwinly | 7% | n/a |
| Laufer | 6% | n/a |
| Mallory | 6% | n/a |
| Lickskillet | 6% | n/a |
| Nims | 5% | n/a |
| Schuelke | 5% | n/a |
How we count · survey areas WA603 (2025-08-28)
What the numbers mean here
Clay swell averages a linear extensibility of 4.3% by land area here, and 30% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 29% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 29% of Asotin County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 16.20 in, 0.65 in below the 1991-2020 average year of 16.85 in.
USDA rates 97% of the land very limited for septic absorption fields.
Drought
100% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 52 of the last 52 weeks; the most was 100% of its area, in 52 weeks, most recently on the October 13, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 100% |
| D2 severe or worse | 100% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
1 flood losses since 2016, $38,815 paid. The worst year was 2017, with 1.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 1 |
| 2018 | 0 |
| 2019 | 0 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 16.85 in |
| 12 months to August 2026 | 16.20 in (-0.65) |
| 2025 | 12.94 in (-3.91) |
| Wettest year since 1895 | 1995: 23.60 in |
| Driest year since 1895 | 1935: 11.05 in |
| Days with 1 inch or more, normal at ASOTIN 14 SW (2 mi away) | 0.6 |
Homes
| Housing units | 10,183 |
| Median year built | 1976 |
| Built before 1980 | 57% |
| Built 2000 or later | 20% |
| Owner-occupied | 73% |
| Median value, owner-occupied | $325,600 |
| Single-family detached | 74% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Garfield County, WA | 23 mi | 13% | 2% |
| Nez Perce County, ID | 24 mi | 7% | 15% |
| Columbia County, WA | 33 mi | under 1% | 4% |
| Lewis County, ID | 39 mi | 23% | 33% |
| Wallowa County, OR | 41 mi | 31% | 11% |
| Latah County, ID | 50 mi | 5% | 43% |
| Whitman County, WA | 52 mi | 1% | 15% |
| Walla Walla County, WA | 60 mi | 0% | 4% |
Sources: USDA SSURGO (August 28, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status