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Stanislaus County, California

Shrink-swell clay limits houses without basements on 24% of Stanislaus County's mapped land, a higher share than 75% of US counties. A shallow water table limits basements on 7%.

The soil survey maps 89% of the county's land area; these shares describe the mapped part. None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 26 flood losses here since 2016. 48% of homes were built before 1980, against 50% nationally; the median home dates from 1981.

Data as of October 13, 2026 · sources

24%

expansive clay: shrink-swell limits slab homes

7%

high water table: limits basements

0%

in drought, October 13, 2026

48%

of homes built before 1980

Soil under Stanislaus County

Expansive clay (limits slab homes)24.4%
High water table (limits basements)7.4%
Septic fields very limited79.6%
Clay swell (LEP, by area)4.0%
High-swell land (LEP 6%+)21.9%
Mapped soil848,608 acres
Soil seriesShare hereSeries nationally: expansive clay
Pentz7%n/a
Dinuba5%n/a
Wisflat4%n/a
Honker4%n/a
Peters4%n/a
Arburua3%n/a
San Joaquin County: 30%Merced County: 28%Santa Clara County: 24%Alameda County: 38%Calaveras County: 2%Contra Costa County: 48%Mariposa County: 5%Amador County: 1%Stanislaus County San JoaquinMercedSanta ClaraAlamedaCalaverasContra CostaMariposaAmadorStanislaus
Stanislaus 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 CA632 (2025-09-08), CA642 (2025-09-08), CA644 (2025-09-02)

What the numbers mean here

Clay swell averages a linear extensibility of 4.0% by land area here, and 22% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 24% of the mapped land.

Rain over the 12 months to August 2026: 14.35 in, 0.18 in above the 1991-2020 average year of 14.17 in.

USDA rates 80% 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.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse29.9%
D1 moderate drought or worse0%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

26 flood losses since 2016, $337,281 paid. The worst year was 2017, with 17.

YearFlood losses
20160
201717
20180
20190
20201
20211
20221
20235
20240
20251
2026 to date0

Rain

Average year, 1991-202014.17 in
12 months to August 202614.35 in (+0.18)
202513.45 in (-0.72)
Wettest year since 18951983: 28.05 in
Driest year since 18952013: 4.37 in
Days with 1 inch or more, normal at MODESTO CITY CO AP (5 mi away)1

Homes

Housing units185,149
Median year built1981
Built before 198048%
Built 2000 or later21%
Owner-occupied61%
Median value, owner-occupied$450,100
Single-family detached76%

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
San Joaquin County, CA 30 mi 30% 23%
Merced County, CA 30 mi 28% 27%
Santa Clara County, CA 44 mi 24% 3%
Alameda County, CA 50 mi 38% 8%
Calaveras County, CA 50 mi 2% 2%
Contra Costa County, CA 57 mi 48% 11%
Mariposa County, CA 60 mi 5% 3%
Amador County, CA 64 mi 1% 3%

Sources: USDA SSURGO (September 8, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status