Frost line depth in Contra Costa County, CA

How deep the ground freezes in Contra Costa County, CA

2 in. Dig to 12 in, the 12 in code minimum. Nearest NOAA station: Mt Diablo Junction, 3 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.