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San Luis Obispo County, California

Shrink-swell clay limits houses without basements on 17% of San Luis Obispo County's mapped land, a higher share than 67% of US counties. A shallow water table limits basements on 1%.

The soil survey maps 77% 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 138 flood losses here since 2016, 4% of them in buildings with basements. 44% of homes were built before 1980, against 50% nationally; the median home dates from 1983.

Data as of October 13, 2026 · sources

17%

expansive clay: shrink-swell limits slab homes

1%

high water table: limits basements

0%

in drought, October 13, 2026

44%

of homes built before 1980

Soil under San Luis Obispo County

Expansive clay (limits slab homes)17.4%
High water table (limits basements)1.3%
Septic fields very limited73.5%
Clay swell (LEP, by area)4.3%
High-swell land (LEP 6%+)18.2%
Mapped soil1,621,822 acres
Soil seriesShare hereSeries nationally: expansive clay
Nacimiento5%n/a
Los Osos4%n/a
Balcom3%n/a
Diablo3%n/a
Lodo3%n/a
Unnamed2%n/a
Kings County: 32%Santa Barbara County: 12%Monterey County: 15%San Benito County: 21%Kern County: 6%Ventura County: 12%Fresno County: 14%Tulare County: 14%San Luis Obispo County KingsSanta BarbaraMontereySan BenitoKernVenturaFresnoTulareSan Luis Obispo
San Luis Obispo 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 CA664 (2025-09-08), CA665 (2025-09-02), CA667 (2025-08-29)

What the numbers mean here

Clay swell averages a linear extensibility of 4.3% by land area here, and 18% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 17% of the mapped land.

Rain over the 12 months to August 2026: 20.05 in, 2.98 in above the 1991-2020 average year of 17.07 in.

USDA rates 74% 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 worse0%
D1 moderate drought or worse0%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

138 flood losses since 2016, $4.2 million paid. The worst year was 2023, with 103. Foundations of the buildings, where recorded: 4% basements, 62% slabs, 27% crawl spaces, 7% elevated. Median water depth outside the building: 10 in.

YearFlood losses
20165
201719
20182
20192
20200
20214
20220
2023103
20241
20250
2026 to date2

Rain

Average year, 1991-202017.07 in
12 months to August 202620.05 in (+2.98)
202518.76 in (+1.69)
Wettest year since 18951941: 35.10 in
Driest year since 18952013: 3.12 in
Days with 1 inch or more, normal at SALINAS DAM (5 mi away)6.6

Homes

Housing units125,669
Median year built1983
Built before 198044%
Built 2000 or later24%
Owner-occupied62%
Median value, owner-occupied$824,700
Single-family detached68%

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
Kings County, CA 59 mi 32% 33%
Santa Barbara County, CA 63 mi 12% 4%
Monterey County, CA 76 mi 15% 2%
San Benito County, CA 92 mi 21% 4%
Kern County, CA 97 mi 6% 1%
Ventura County, CA 103 mi 12% 4%
Fresno County, CA 105 mi 14% 2%
Tulare County, CA 110 mi 14% 1%

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