Frost line depth in Hartley County, TX
How deep the ground freezes in Hartley County, TX
18 in. Dig to 18 in, just below the frost. Nearest NOAA station: Dalhart 6 Sw, 11.5 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.