By giving property rights to the county's Department of Parks, Open Space & Cultural Development, Hetfield is guaranteed the land will be preserved and its care will be the responsibility of the county.

The area includes a highly visible ridge line separating Lucas Valley to the north and portions of the upper Ross Valley and San Geronimo Valley.

Hetfield and his wife, Francesca, plan to build a 14,000-square-foot house, swimming pool and another 6,000-square-foot building that would house a music studio, garage and caretaker's residence on part of the land they kept for development.

"I'm very excited about this easement and I consider it to be a generous offer on the part of the Hetfields," Supervisor Steve Kinsey said Tuesday. "It puts another nail in the coffin for suburban sprawl in Lucas Valley."