Union County, Oregon
Shrink-swell clay limits houses without basements on 26% of Union County's mapped land, a higher share than 77% of US counties and the 9th highest of 35 Oregon counties. A shallow water table limits basements on 21%.
The soil survey maps 52% 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 6 flood losses here since 2016. 61% of homes were built before 1980, against 50% nationally; the median home dates from 1973.
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 Union County
| Expansive clay (limits slab homes) | 26.5% |
| High water table (limits basements) | 20.7% |
| Septic fields very limited | 95.1% |
| Clay swell (LEP, by area) | 4.3% |
| High-swell land (LEP 6%+) | 28.5% |
| Mapped soil | 671,305 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Tolo | 12% | n/a |
| Klicker | 11% | n/a |
| Gwinly | 8% | n/a |
| Anatone | 5% | n/a |
| Lookingglass | 4% | n/a |
| Hall Ranch | 4% | n/a |
How we count · survey areas OR625 (2025-09-10)
What the numbers mean here
Clay swell averages a linear extensibility of 4.3% by land area here, and 29% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 26% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 26% of Union County's mapped land has shrink-swell clay.
On 21% of Union County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.
Rain over the 12 months to August 2026: 24.14 in, 4.64 in below the 1991-2020 average year of 28.78 in.
USDA rates 95% 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 | 55.5% |
| D4 exceptional | 0% |
Flood losses since 2016
6 flood losses since 2016, $74,217 paid. The worst year was 2020, with 3.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 0 |
| 2019 | 2 |
| 2020 | 3 |
| 2021 | 1 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 28.78 in |
| 12 months to August 2026 | 24.14 in (-4.64) |
| 2025 | 25.13 in (-3.65) |
| Wettest year since 1895 | 1984: 38.40 in |
| Driest year since 1895 | 1935: 17.79 in |
| Days with 1 inch or more, normal at WALLOWA (29 mi away) | 0.8 |
Homes
| Housing units | 11,829 |
| Median year built | 1973 |
| Built before 1980 | 61% |
| Built 2000 or later | 16% |
| Owner-occupied | 66% |
| Median value, owner-occupied | $294,600 |
| Single-family detached | 70% |
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 |
|---|---|---|---|
| Umatilla County, OR | 41 mi | 7% | 3% |
| Baker County, OR | 44 mi | 47% | 7% |
| Wallowa County, OR | 44 mi | 31% | 11% |
| Columbia County, WA | 69 mi | under 1% | 4% |
| Walla Walla County, WA | 70 mi | 0% | 4% |
| Asotin County, WA | 71 mi | 29% | 5% |
| Grant County, OR | 75 mi | 15% | 4% |
| Morrow County, OR | 78 mi | 7% | 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