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Santa Clara County, California

Shrink-swell clay limits houses without basements on 24% of Santa Clara County's mapped land, a higher share than 74% of US counties. A shallow water table limits basements on 3%.

None of the county is in drought on the September 22, 2026 Drought Monitor map. FEMA's flood data list 260 flood losses here since 2016, 25% of them in buildings with basements. 60% of homes were built before 1980, against 50% nationally; the median home dates from 1975.

Data as of September 22, 2026 · sources

24%

expansive clay: shrink-swell limits slab homes

3%

high water table: limits basements

0%

in drought, September 22, 2026

60%

of homes built before 1980

Soil under Santa Clara County

Expansive clay (limits slab homes)23.6%
High water table (limits basements)2.6%
Septic fields very limited79.8%
Clay swell (LEP, by area)3.9%
High-swell land (LEP 6%+)20.1%
Urban land, not rated12.4%
Mapped soil856,841 acres
Soil seriesShare hereSeries nationally: expansive clay
Gaviota21%n/a
Vallecitos11%n/a
Los Gatos7%n/a
Mouser2%n/a
Los Osos2%n/a
Sanikara2%n/a
Santa Cruz County: 10%Alameda County: 38%San Mateo County: 10%Stanislaus County: 24%Contra Costa County: 48%Merced County: 28%San Benito County: 21%San Joaquin County: 30%Santa Clara County Santa CruzAlamedaSan MateoStanislausContra CostaMercedSan BenitoSan JoaquinSanta Clara
Santa Clara 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 CA641 (2025-08-29), CA646 (2025-08-29)

What the numbers mean here

Clay swell averages a linear extensibility of 3.9% by land area here, and 20% 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: 21.11 in, 2.82 in below the 1991-2020 average year of 23.93 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 September 22, 2026 map. No part of the county was in drought in the last 52 weeks.

September 30, 2025Share of area in drought, weeklySeptember 22, 2026
Category, September 22, 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

260 flood losses since 2016, $8.6 million paid. The worst year was 2017, with 188. Foundations of the buildings, where recorded: 25% basements, 32% slabs, 35% crawl spaces, 8% elevated. Median water depth outside the building: 10 in.

YearFlood losses
20165
2017188
20181
20195
20205
20213
202215
202334
20243
20251
2026 to date0

Rain

Average year, 1991-202023.93 in
12 months to August 202621.11 in (-2.82)
202521.20 in (-2.73)
Wettest year since 18951983: 46.71 in
Driest year since 18952013: 5.12 in
Days with 1 inch or more, normal at MT HAMILTON (9 mi away)6.5

Homes

Housing units698,837
Median year built1975
Built before 198060%
Built 2000 or later20%
Owner-occupied55%
Median value, owner-occupied$1.5 million
Single-family detached51%

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
Santa Cruz County, CA 23 mi 10% 1%
Alameda County, CA 31 mi 38% 8%
San Mateo County, CA 40 mi 10% 3%
Stanislaus County, CA 44 mi 24% 7%
Contra Costa County, CA 50 mi 48% 11%
Merced County, CA 53 mi 28% 27%
San Benito County, CA 54 mi 21% 4%
San Joaquin County, CA 54 mi 30% 23%

Sources: USDA SSURGO (August 29, 2025) · US Drought Monitor (September 22, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status