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Riverside County, California
USDA's soil survey flags shrink-swell clay on 3% of Riverside County's mapped land and a shallow water table under basements on 5%, both below the national shares of 15% and 29%. The soil survey maps 57% of the county's land area; these shares describe the mapped part.
48.6% of the county is in drought on the September 22, 2026 Drought Monitor map. FEMA's flood data list 195 flood losses here since 2016, 4% of them in buildings with basements. 30% of homes were built before 1980, against 50% nationally; the median home dates from 1990.
Data as of September 22, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, September 22, 2026
of homes built before 1980
Soil under Riverside County
| Expansive clay (limits slab homes) | 2.8% |
| High water table (limits basements) | 5.0% |
| Septic fields very limited | 72.3% |
| Clay swell (LEP, by area) | 1.8% |
| High-swell land (LEP 6%+) | 3.7% |
| Mapped soil | 2,639,184 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Cieneba | 5% | n/a |
| Pintobasin | 3% | n/a |
| Carsitas | 3% | n/a |
| Carrizo | 3% | n/a |
| Myoma | 2% | n/a |
| Blackeagle | 2% | n/a |
How we count · survey areas AZ656 (2025-08-27), CA678 (2025-09-08), CA679 (2025-09-08), CA680 (2025-09-08), CA681 (2025-09-08), CA794 (2025-09-08)
What the numbers mean here
Rain over the 12 months to August 2026: 6.86 in, 1.12 in below the 1991-2020 average year of 7.98 in.
USDA rates 72% of the land very limited for septic absorption fields.
With shrink-swell clay on 3% and a shallow water table on 5% of the land, the soil survey points to neither problem across most of Riverside County; conditions still vary lot by lot.
Drought
48.6% of the county is in drought (D1 or worse) on the September 22, 2026 map. Part of the county was in drought in 29 of the last 52 weeks; the most was 100% of its area, in 7 weeks, most recently on the November 11, 2025 map.
| Category, September 22, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 74.4% |
| D1 moderate drought or worse | 48.6% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
195 flood losses since 2016, $5.8 million paid. The worst year was 2023, with 74. Foundations of the buildings, where recorded: 4% basements, 90% slabs, 5% crawl spaces, 1% elevated. Median water depth outside the building: 6.5 in.
| Year | Flood losses |
|---|---|
| 2016 | 18 |
| 2017 | 27 |
| 2018 | 15 |
| 2019 | 27 |
| 2020 | 11 |
| 2021 | 5 |
| 2022 | 5 |
| 2023 | 74 |
| 2024 | 2 |
| 2025 | 9 |
| 2026 to date | 2 |
Rain
| Average year, 1991-2020 | 7.98 in |
| 12 months to August 2026 | 6.86 in (-1.12) |
| 2025 | 7.99 in (+0.01) |
| Wettest year since 1895 | 1978: 18.15 in |
| Driest year since 1895 | 1953: 2.72 in |
| Days with 1 inch or more, normal at DESERT RESORTS RGNL AP (17 mi away) | 0.3 |
Homes
| Housing units | 869,414 |
| Median year built | 1990 |
| Built before 1980 | 30% |
| Built 2000 or later | 36% |
| Owner-occupied | 69% |
| Median value, owner-occupied | $557,300 |
| Single-family detached | 69% |
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 |
|---|---|---|---|
| Imperial County, CA | 63 mi | n/a | n/a |
| San Diego County, CA | 72 mi | 17% | 1% |
| San Bernardino County, CA | 74 mi | 1% | under 1% |
| Orange County, CA | 105 mi | 14% | 3% |
| La Paz County, AZ | 110 mi | 2% | under 1% |
| Los Angeles County, CA | 135 mi | 4% | under 1% |
| Yuma County, AZ | 137 mi | 1% | under 1% |
| Clark County, NV | 175 mi | under 1% | under 1% |
Sources: USDA SSURGO (September 8, 2025) · US Drought Monitor (September 22, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status