Montrose County, CO: the USDA septic-suitability picture
Very limited
Montrose County, CO's SSURGO dominant class comes back "Very limited", covering 87.6% of the county. Practically, that rules out a simple gravity system for most of the county - 87.6% of it sits in USDA's most-constrained bucket. For scale: 2,240.946 square miles and 44,806 people call Montrose County home.
Before you rely on this for one lot
Two lots a mile apart in Montrose County can carry different soil, even though they share one countywide rating. The real answer for one lot is still a site-specific perc test, running about $750-$1,850 (typically near $1,300).
Budgeting for a system in Montrose County, CO
Montrose County's soil reading pushes the likely outcome toward an engineered system rather than a conventional one. Conventional systems run $3,000-$8,000 where they pass; where they don't, engineered alternatives (mound or aerobic treatment, whichever the health department requires) run $10,000-$40,000 - budget toward the higher figure until a perc test says otherwise.
Where this sits nationally
Among the 3,058 rated counties on this site, Montrose County, CO ranks 1,500 most-constrained nationally, and 27 of 63 within Colorado.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems