Frost line depth in Umatilla County, OR
How deep the ground freezes in Umatilla County, OR
15 in. Dig to 15 in, just below the frost. Nearest NOAA station: Pendleton Dwtn, 6.2 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.