The Marin County Board of Supervisors unanimously accepted the donation Tuesday. It follows Hetfield's earlier gift to the county of more than 400 acres for open space. Both plots of land are around Hetfield's home.
Hetfield's land use consultant, Scott Hochstrasser, says the donations reflect the singer's desire to maintain privacy and preserve open space.
Meanwhile, county officials say they are close to a deal with Hetfield that would reroute a hiking trail that crosses his property. The project is expected to cost the county more than $200,000.
Hetfield recently constructed a fence to block use of the trail.