Gilliam County, Oregon
USDA's soil survey flags shrink-swell clay on 3% of Gilliam County's mapped land and a shallow water table under basements on under 1%, both below the national shares of 15% and 29%. 40.7% of the county is in drought on the October 13, 2026 Drought Monitor map.
FEMA's flood data list no flood losses here since 2016. 63% of homes were built before 1980, against 50% nationally; the median home dates from 1961.
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 Gilliam County
| Expansive clay (limits slab homes) | 3.3% |
| High water table (limits basements) | 0.1% |
| Septic fields very limited | 79.8% |
| Clay swell (LEP, by area) | 2.1% |
| High-swell land (LEP 6%+) | 3.4% |
| Mapped soil | 782,630 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Lickskillet | 13% | n/a |
| Ritzville | 11% | n/a |
| Morrow | 7% | n/a |
| Bakeoven | 6% | n/a |
| Condon | 6% | n/a |
| Mikkalo | 6% | n/a |
How we count · survey areas OR021 (2025-09-10)
What the numbers mean here
Rain over the 12 months to August 2026: 10.95 in, 0.45 in below the 1991-2020 average year of 11.40 in.
USDA rates 80% of the land very limited for septic absorption fields.
With shrink-swell clay on 3% and a shallow water table on under 1% of the land, the soil survey points to neither problem across most of Gilliam County; conditions still vary lot by lot.
Drought
40.7% 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 41.2% of its area, on the April 14, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 40.7% |
| D2 severe or worse | 14.6% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Gilliam County since 2016.
Rain
| Average year, 1991-2020 | 11.40 in |
| 12 months to August 2026 | 10.95 in (-0.45) |
| 2025 | 11.66 in (+0.26) |
| Wettest year since 1895 | 1996: 17.53 in |
| Driest year since 1895 | 1939: 6.05 in |
| Days with 1 inch or more, normal at MORO (23 mi away) | 0.3 |
Homes
| Housing units | 1,138 |
| Median year built | 1961 |
| Built before 1980 | 63% |
| Built 2000 or later | 17% |
| Owner-occupied | 74% |
| Median value, owner-occupied | $189,300 |
| Single-family detached | 79% |
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 |
|---|---|---|---|
| Sherman County, OR | 20 mi | 0% | 1% |
| Morrow County, OR | 33 mi | 7% | 1% |
| Klickitat County, WA | 42 mi | 2% | 5% |
| Wasco County, OR | 46 mi | 15% | 2% |
| Wheeler County, OR | 46 mi | 27% | 1% |
| Jefferson County, OR | 67 mi | 29% | 1% |
| Hood River County, OR | 67 mi | 0% | 5% |
| Benton County, WA | 69 mi | 0% | 1% |
Sources: USDA SSURGO (September 10, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status