Marin County, CA Shrink-Swell Risk

Shrink-swell potential in Marin County, CA

Moderate

Soil across 53.2% of Marin County, CA comes back "Moderate" in USDA's shrink-swell data, averaging 3.21% linear extensibility. That's a middle reading: not the sharp swings that crack a foundation outright, but enough that grading and drainage are worth getting right.

What this number does and doesn't tell you

This is a countywide, area-weighted figure across every soil survey map unit in Marin County, CA - never a reading for one specific parcel. A local geotechnical report, typically $1,000-$5,000 (around $2,700 typical), is the only way to know what one lot in Marin County will actually do.

Marin County: the real numbers

Marin County's soil reading points toward standard foundation practice as the likely outcome, not the exception. A geotechnical report runs $1,000-$5,000, typically around $2,700. Foundation repair, if a specific lot turns out to differ from the county average, runs $5,000-$15,000.

Where this sits nationally

Among the 3,085 rated counties on this site, Marin County, CA ranks 1,039 most-constrained nationally, and 19 of 58 within California. Marin County covers 520 square miles and counts 256,400 residents.

Before you act on this

Orleans Parish, LA carries this site's most-constrained reading. Dorchester County, MD and Canadian County, OK are worth a look for comparison.

How this reading is built, and its real limits · Moisture management: the cheap fix that works on any soil

Elsewhere in California

Every county in California is on this site, including Alameda County, CA and Trinity County, CA. The full underlying dataset is downloadable directly, one row per county.