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Yolo County, California
Shrink-swell clay limits houses without basements on 44% of Yolo County's mapped land, a higher share than 88% of US counties and the 4th highest of 54 California counties. A shallow water table limits basements on 23%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 41 flood losses here since 2016, 0% of them in buildings with basements. 45% of homes were built before 1980, against 50% nationally; the median home dates from 1983.
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 Yolo County
| Expansive clay (limits slab homes) | 43.8% |
| High water table (limits basements) | 23.0% |
| Septic fields very limited | 81.8% |
| Clay swell (LEP, by area) | 7.0% |
| High-swell land (LEP 6%+) | 48.7% |
| Mapped soil | 650,172 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Sacramento | 8% | n/a |
| Capay | 6% | n/a |
| Balcom | 6% | n/a |
| Yolo | 6% | n/a |
| Sycamore | 6% | n/a |
| Sehorn | 5% | n/a |
How we count · survey areas CA113 (2025-09-03)
What the numbers mean here
Clay swell averages a linear extensibility of 7.0% by land area here, and 49% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 44% of the mapped land.
On 23% of Yolo 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: 18.85 in, 2.50 in below the 1991-2020 average year of 21.35 in.
USDA rates 82% of the land very limited for septic absorption fields.
Drought
0% of the county is in drought (D1 or worse) on the October 13, 2026 map. No part of the county was in drought in the last 52 weeks.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 96% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
41 flood losses since 2016, $626,864 paid. The worst year was 2019, with 17. Foundations of the buildings, where recorded: 68% slabs, 28% crawl spaces, 4% elevated. Median water depth outside the building: 5 in.
| Year | Flood losses |
|---|---|
| 2016 | 2 |
| 2017 | 12 |
| 2018 | 1 |
| 2019 | 17 |
| 2020 | 0 |
| 2021 | 1 |
| 2022 | 1 |
| 2023 | 6 |
| 2024 | 1 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 21.35 in |
| 12 months to August 2026 | 18.85 in (-2.50) |
| 2025 | 17.75 in (-3.60) |
| Wettest year since 1895 | 1983: 42.62 in |
| Driest year since 1895 | 2013: 5.79 in |
| Days with 1 inch or more, normal at WOODLAND 1 WNW (6 mi away) | 4.8 |
Homes
| Housing units | 82,447 |
| Median year built | 1983 |
| Built before 1980 | 45% |
| Built 2000 or later | 28% |
| Owner-occupied | 54% |
| Median value, owner-occupied | $620,700 |
| Single-family detached | 58% |
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 |
|---|---|---|---|
| Napa County, CA | 26 mi | 14% | 6% |
| Sutter County, CA | 27 mi | 41% | 37% |
| Solano County, CA | 29 mi | 50% | 21% |
| Sacramento County, CA | 34 mi | 16% | 26% |
| Colusa County, CA | 39 mi | 55% | 37% |
| Yuba County, CA | 51 mi | 21% | 5% |
| Contra Costa County, CA | 53 mi | 48% | 11% |
| Lake County, CA | 54 mi | 8% | 1% |
Sources: USDA SSURGO (September 3, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status