Ronald Reagan adviser William P. Clark Jr. dead at 81 SHANDON, Calif., Aug. 12 (UPI) -- William P. Clark Jr., who served as U.S. interior secretary in President Reagan's administration, has died of Parkinson's disease, his son said. Clark died at his home in Shandon, Calif., Saturday, The (San Luis Obispo) Tribune Besides serving as interior secretary, Clark also was , the newspaper noted. Clark, a cattle rancher, was a close friend of Reagan, who also appointed him to a judgeship when the future president was governor of California. "We love him and are going to miss him a lot," his son, Paul Clark, said.