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Tuolumne County, California

USDA's soil survey flags shrink-swell clay on 1% of Tuolumne County's mapped land and a shallow water table under basements on 2%, 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 11 flood losses here since 2016. 50% of homes were built before 1980, against 50% nationally; the median home dates from 1980.

Data as of October 13, 2026 · sources

1%

expansive clay: shrink-swell limits slab homes

2%

high water table: limits basements

0%

in drought, October 13, 2026

50%

of homes built before 1980

Soil under Tuolumne County

Expansive clay (limits slab homes)1.3%
High water table (limits basements)2.2%
Septic fields very limited74.1%
Clay swell (LEP, by area)2.4%
High-swell land (LEP 6%+)1.4%
Mapped soil2,105,863 acres
Soil seriesShare hereSeries nationally: expansive clay
Loafercreek4%n/a
Canisrocks3%n/a
Nedsgulch3%n/a
Bonanza3%n/a
Copperopolis2%n/a
Gopheridge2%n/a
Mariposa County: 5%Calaveras County: 2%Alpine County: 2%Amador County: 1%Madera County: 2%Mono County: 3%El Dorado County: 1%Douglas County: 20%Tuolumne County MariposaCalaverasAlpineAmadorMaderaMonoEl DoradoDouglasTuolumne
Tuolumne County (heavy outline) and nearby counties, shaded by expansive clay share.under 10%10-25%25-40%40-60%60%+

How we count · survey areas CA630 (2025-09-02), CA731 (2025-09-02), CA790 (2025-09-02)

What the numbers mean here

Rain over the 12 months to August 2026: 36.47 in, 4.49 in below the 1991-2020 average year of 40.96 in.

USDA rates 74% of the land very limited for septic absorption fields.

With shrink-swell clay on 1% and a shallow water table on 2% of the land, the soil survey points to neither problem across most of Tuolumne County; conditions still vary lot by lot.

Drought

0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 1 of the last 52 weeks; the most was 1.5% of its area, on the April 7, 2026 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse100%
D1 moderate drought or worse0%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

11 flood losses since 2016, $267,444 paid. The worst year was 2023, with 9.

YearFlood losses
20160
20170
20181
20191
20200
20210
20220
20239
20240
20250
2026 to date0

Rain

Average year, 1991-202040.96 in
12 months to August 202636.47 in (-4.49)
202539.11 in (-1.85)
Wettest year since 18951983: 79.26 in
Driest year since 18952013: 12.64 in
Days with 1 inch or more, normal at CHERRY VALLEY DAM (4 mi away)16.7

Homes

Housing units31,589
Median year built1980
Built before 198050%
Built 2000 or later13%
Owner-occupied74%
Median value, owner-occupied$433,200
Single-family detached80%

What repairs cost

Published ranges from cost guides, not quotes. More sources, and where they disagree.

WorkRangeSource
Foundation repair, US $2,200 to $8,200 Fixr, January 27, 2026
Pier-and-beam repair, US $2,000 to $15,000 Fixr, January 27, 2026
Foundation inspection, US $300 to $600 Fixr, January 31, 2025

Nearby counties

PlaceDistanceExpansive clayHigh water table
Mariposa County, CA 31 mi 5% 3%
Calaveras County, CA 34 mi 2% 2%
Alpine County, CA 41 mi 2% 7%
Amador County, CA 47 mi 1% 3%
Madera County, CA 58 mi 2% 3%
Mono County, CA 60 mi 3% 7%
El Dorado County, CA 61 mi 1% 2%
Douglas County, NV 64 mi 20% 9%

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