Frost line depth in Powell County, MT
How deep the ground freezes in Powell County, MT
54 in. Dig to 55 in, just below the frost. Nearest NOAA station: Ovando 9 Sse, 6.5 mi.
Your building department sets the legal frost line depth (IRC Table R301.2(1)); footings must go below it (R403.1.4.1). Call them before you dig.