Mariposa County, CA Fence Regulations: Retaining Walls (2026)

Mariposa County is entirely unincorporated, so retaining-wall permits are issued by the County Building Department applying the California Residential Building Code. A retaining wall is exempt from a building permit only when it is not over 4 feet high, measured from the bottom of the footing to the top of the wall, and is not supporting a surcharge (such as a slope load, driveway, or structure above). A taller wall, or one carrying a surcharge, requires a building permit and typically engineered plans. In the adopted Mariposa Town Planning Area, retaining walls that are not part of a building or structure are expressly listed among the uses permitted within required setback areas (Mariposa County Code Section 17.336.010.C), so a low retaining wall may sit in a yard setback where a building could not. Retaining walls used to reduce the Highway 49 North right-of-way are also specifically contemplated in the code (Section 17.336.017). Hillside and grading provisions in the same chapter can apply when a wall is part of larger earthwork. Confirm height, surcharge, and engineering needs with the Building Department before construction.