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Colusa County, California

Shrink-swell clay limits houses without basements on 55% of Colusa County's mapped land, a higher share than 93% of US counties and the highest of 54 California counties. A shallow water table limits basements on 37%.

None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 25 flood losses here since 2016. 52% of homes were built before 1980, against 50% nationally; the median home dates from 1978.

Data as of October 13, 2026 · sources

55%

expansive clay: shrink-swell limits slab homes

37%

high water table: limits basements

0%

in drought, October 13, 2026

52%

of homes built before 1980

Soil under Colusa County

Expansive clay (limits slab homes)55.0%
High water table (limits basements)36.9%
Septic fields very limited93.7%
Clay swell (LEP, by area)6.2%
High-swell land (LEP 6%+)53.5%
Mapped soil738,831 acres
Soil seriesShare hereSeries nationally: expansive clay
Willows15%n/a
Millsholm9%n/a
Capay7%n/a
Westfan5%n/a
Vina4%n/a
Contra Costa4%n/a
Lake County: 8%Sutter County: 41%Glenn County: 38%Yolo County: 44%Napa County: 14%Butte County: 31%Yuba County: 21%Sonoma County: 22%Colusa County LakeSutterGlennYoloNapaButteYubaSonomaColusa
Colusa 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 CA011 (2025-09-03)

What the numbers mean here

Clay swell averages a linear extensibility of 6.2% by land area here, and 53% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 55% of the mapped land.

On 37% of Colusa County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.

Rain over the 12 months to August 2026: 22.60 in, 2.17 in below the 1991-2020 average year of 24.77 in.

USDA rates 94% 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 worse100%
D1 moderate drought or worse0%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

25 flood losses since 2016, $908,676 paid. The worst year was 2017, with 20.

YearFlood losses
20161
201720
20180
20193
20200
20210
20220
20230
20241
20250
2026 to date0

Rain

Average year, 1991-202024.77 in
12 months to August 202622.60 in (-2.17)
202518.60 in (-6.17)
Wettest year since 18951983: 50.74 in
Driest year since 18951976: 6.31 in
Days with 1 inch or more, normal at COLUSA 2 SSW (11 mi away)2.3

Homes

Housing units8,211
Median year built1978
Built before 198052%
Built 2000 or later25%
Owner-occupied62%
Median value, owner-occupied$393,400
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
Lake County, CA 28 mi 8% 1%
Sutter County, CA 30 mi 41% 37%
Glenn County, CA 31 mi 38% 15%
Yolo County, CA 39 mi 44% 23%
Napa County, CA 47 mi 14% 6%
Butte County, CA 48 mi 31% 27%
Yuba County, CA 48 mi 21% 5%
Sonoma County, CA 58 mi 22% 5%

Sources: USDA SSURGO (September 3, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status