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Columbia County, Washington

USDA's soil survey flags shrink-swell clay on under 1% of Columbia County's mapped land and a shallow water table under basements on 4%, both below the national shares of 15% and 29%. The soil survey maps 72% 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 16 flood losses here since 2016. 73% of homes were built before 1980, against 50% nationally; the median home dates from 1953.

Data as of October 13, 2026 · sources

<1%

expansive clay: shrink-swell limits slab homes

4%

high water table: limits basements

100%

in drought, October 13, 2026

73%

of homes built before 1980

Soil under Columbia County

Expansive clay (limits slab homes)0.2%
High water table (limits basements)4.2%
Septic fields very limited89.6%
Clay swell (LEP, by area)2.2%
High-swell land (LEP 6%+)0.2%
Mapped soil399,591 acres
Soil seriesShare hereSeries nationally: expansive clay
Athena18%n/a
Walla Walla17%n/a
Palouse6%n/a
Kuhl5%n/a
Tolo4%n/a
Gwin4%n/a
Garfield County: 13%Walla Walla County: 0%Asotin County: 29%Whitman County: 1%Franklin County: 0%Nez Perce County: 7%Adams County: 0%Wallowa County: 31%Columbia County GarfieldWalla WallaAsotinWhitmanFranklinNez PerceAdamsWallowaColumbia
Columbia County (heavy outline) and nearby counties, shaded by expansive clay share.under 10%10-25%25-40%40-60%60%+

How we count · survey areas WA613 (2025-08-28)

What the numbers mean here

Rain over the 12 months to August 2026: 25.41 in, 1.25 in below the 1991-2020 average year of 26.66 in.

USDA rates 90% of the land very limited for septic absorption fields.

With shrink-swell clay on under 1% and a shallow water table on 4% of the land, the soil survey points to neither problem across most of Columbia County; conditions still vary lot by lot.

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 41 weeks, most recently on the October 13, 2026 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse100%
D1 moderate drought or worse100%
D2 severe or worse54.4%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

16 flood losses since 2016, $351,854 paid. The worst year was 2020, with 9.

YearFlood losses
20160
20171
20180
20190
20209
20210
20220
20231
20240
20250
2026 to date5

Rain

Average year, 1991-202026.66 in
12 months to August 202625.41 in (-1.25)
202523.81 in (-2.85)
Wettest year since 18951996: 40.17 in
Driest year since 18951952: 17.38 in
Days with 1 inch or more, normal at DAYTON 1 WSW (5 mi away)1

Homes

Housing units2,217
Median year built1953
Built before 198073%
Built 2000 or later17%
Owner-occupied78%
Median value, owner-occupied$271,200
Single-family detached82%

What repairs cost

Published ranges from cost guides, not quotes. More sources, and where they disagree.

WorkRangeSource
Foundation repair, US $2,200 to $8,200 Fixr, January 27, 2026
Pier-and-beam repair, US $2,000 to $15,000 Fixr, January 27, 2026
Foundation inspection, US $300 to $600 Fixr, January 31, 2025

Nearby counties

PlaceDistanceExpansive clayHigh water table
Garfield County, WA 20 mi 13% 2%
Walla Walla County, WA 28 mi 0% 4%
Asotin County, WA 33 mi 29% 5%
Whitman County, WA 46 mi 1% 15%
Franklin County, WA 51 mi 0% under 1%
Nez Perce County, ID 54 mi 7% 15%
Adams County, WA 57 mi under 1% 2%
Wallowa County, OR 59 mi 31% 11%

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