Septic soil in Plumas County, CA, by the numbers
Very limited
Soil across 92% of Plumas County, CA rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 92% of it sits in USDA's most-constrained bucket. Plumas County, CA is 2,553.062 square miles with a population of 18,834.
What Plumas County's reading doesn't cover
Plumas County's rating is an average across the whole county, not a promise about any one lot inside it. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Plumas County will actually do.
What a system would cost here
With 92% of Plumas County rating "Very limited", a standard gravity system is not a safe assumption here. The engineered-system range, $10,000-$40,000 (mound or aerobic treatment), is the more realistic number to plan around, against $3,000-$8,000 for a conventional system on the rare lot that passes.
How Plumas County, CA compares
Nationally, Plumas County, CA is the 1,045-most-constrained of 3,058 rated counties for septic soil. Within California alone it ranks 26 of 57.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems