What Montezuma County, CO's soil rates for a septic system
Very limited
Soil across 89.9% of Montezuma County, CO rates "Very limited" in USDA's septic-absorption-field interpretation. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 89.9% of Montezuma County's land. Montezuma County, CO is 2,029.349 square miles with a population of 26,841.
What Montezuma County's reading doesn't cover
USDA's survey covers the whole of Montezuma County, CO at once, not any single address. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Montezuma County will actually do.
What a system would cost here
With 89.9% of Montezuma 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.
Where this sits nationally
Nationally, Montezuma County, CO is the 1,278-most-constrained of 3,058 rated counties for septic soil. Within Colorado alone it ranks 18 of 63.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems