The Vails' former ranch, now part of Channel Islands National Park, is no longer a home for cattle, cowboys or adventurous children. And now the family's last link to the place is being severed. For the family that once owned Santa Rosa Island, it was part Zane Grey, part "Robinson Crusoe." Generations of Vail cousins would arrive from the mainland and take refuge for months at a time. They would explore places with pirate-map names: Skull Gulch, Abalone Rocks, China Camp. They were city kids, but they rode with the island's cowboys and knew the island lore — stories about...