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Mendocino County, California

USDA's soil survey flags shrink-swell clay on 9% of Mendocino County's mapped land and a shallow water table under basements on 6%, 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 15 flood losses here since 2016. 57% of homes were built before 1980, against 50% nationally; the median home dates from 1977.

Data as of October 13, 2026 · sources

9%

expansive clay: shrink-swell limits slab homes

6%

high water table: limits basements

0%

in drought, October 13, 2026

57%

of homes built before 1980

Soil under Mendocino County

Expansive clay (limits slab homes)8.6%
High water table (limits basements)5.9%
Septic fields very limited78.6%
Clay swell (LEP, by area)3.5%
High-swell land (LEP 6%+)8.5%
Mapped soil2,332,126 acres
Soil seriesShare hereSeries nationally: expansive clay
Hopland5%n/a
Ornbaun5%n/a
Yorkville5%n/a
Zeni4%n/a
Yellowhound3%n/a
Sheetiron3%n/a
Lake County: 8%Glenn County: 38%Colusa County: 55%Sonoma County: 22%Tehama County: 15%Trinity County: no dataNapa County: 14%Humboldt County: 10%Mendocino County LakeGlennColusaSonomaTehamaTrinityNapaHumboldtMendocino
Mendocino 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 CA687 (2025-09-05), CA694 (2025-09-03), CA709 (2025-09-03)

What the numbers mean here

Rain over the 12 months to August 2026: 50.17 in, 1.73 in below the 1991-2020 average year of 51.90 in.

USDA rates 79% of the land very limited for septic absorption fields.

With shrink-swell clay on 9% and a shallow water table on 6% of the land, the soil survey points to neither problem across most of Mendocino 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 5 of the last 52 weeks; the most was 5.9% of its area, in 4 weeks, most recently on the September 15, 2026 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse91.6%
D1 moderate drought or worse0%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

15 flood losses since 2016, $604,790 paid. The worst year was 2017, with 8.

YearFlood losses
20160
20178
20180
20193
20200
20210
20220
20231
20242
20251
2026 to date0

Rain

Average year, 1991-202051.90 in
12 months to August 202650.17 in (-1.73)
202551.37 in (-0.53)
Wettest year since 18951983: 100.88 in
Driest year since 18952013: 15.50 in
Days with 1 inch or more, normal at POTTER VALLEY POWERHOUSE (17 mi away)14.5

Homes

Housing units41,675
Median year built1977
Built before 198057%
Built 2000 or later14%
Owner-occupied62%
Median value, owner-occupied$512,200
Single-family detached72%

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 43 mi 8% 1%
Glenn County, CA 56 mi 38% 15%
Colusa County, CA 66 mi 55% 37%
Sonoma County, CA 69 mi 22% 5%
Tehama County, CA 80 mi 15% 3%
Trinity County, CA 86 mi n/a n/a
Napa County, CA 87 mi 14% 6%
Humboldt County, CA 92 mi 10% 19%

Sources: USDA SSURGO (September 5, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status