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Mariposa County, California
USDA's soil survey flags shrink-swell clay on 5% of Mariposa County's mapped land and a shallow water table under basements on 3%, both below the national shares of 15% and 29%. None 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. 36% of homes were built before 1980, against 50% nationally; the median home dates from 1986.
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 Mariposa County
| Expansive clay (limits slab homes) | 4.9% |
| High water table (limits basements) | 2.5% |
| Septic fields very limited | 70.9% |
| Clay swell (LEP, by area) | 2.6% |
| High-swell land (LEP 6%+) | 3.5% |
| Mapped soil | 856,650 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Daulton | 5% | n/a |
| Canisrocks | 5% | n/a |
| Gopheridge | 4% | n/a |
| Loafercreek | 4% | n/a |
| Auberry | 3% | n/a |
| Jasperpeak | 3% | n/a |
How we count · survey areas CA649 (2025-09-02), CA731 (2025-09-02), CA790 (2025-09-02)
What the numbers mean here
Rain over the 12 months to August 2026: 29.95 in, 1.40 in below the 1991-2020 average year of 31.35 in.
USDA rates 71% of the land very limited for septic absorption fields.
With shrink-swell clay on 5% and a shallow water table on 3% of the land, the soil survey points to neither problem across most of Mariposa County; conditions still vary lot by lot.
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 | 100% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Mariposa County since 2016.
Rain
| Average year, 1991-2020 | 31.35 in |
| 12 months to August 2026 | 29.95 in (-1.40) |
| 2025 | 33.76 in (+2.41) |
| Wettest year since 1895 | 1983: 61.37 in |
| Driest year since 1895 | 2013: 9.39 in |
| Days with 1 inch or more, normal at EXCHEQUER DAM (19 mi away) | 4.7 |
Homes
| Housing units | 9,836 |
| Median year built | 1986 |
| Built before 1980 | 36% |
| Built 2000 or later | 20% |
| Owner-occupied | 75% |
| Median value, owner-occupied | $387,900 |
| Single-family detached | 75% |
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 |
|---|---|---|---|
| Madera County, CA | 27 mi | 2% | 3% |
| Tuolumne County, CA | 31 mi | 1% | 2% |
| Merced County, CA | 52 mi | 28% | 27% |
| Calaveras County, CA | 55 mi | 2% | 2% |
| Fresno County, CA | 58 mi | 14% | 2% |
| Stanislaus County, CA | 60 mi | 24% | 7% |
| Mono County, CA | 61 mi | 3% | 7% |
| Alpine County, CA | 71 mi | 2% | 7% |
Sources: USDA SSURGO (September 2, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status