MARIPOSA, Calif. - A Northern California family found dead in a remote hiking area died of hyperthermia and probable dehydration, the Mariposa County sheriff announced Thursday.The mysterious deaths of John Gerrish, his wife, Ellen Chung, their 1-year-old daughter, Miju, and their dog baffled authorities for two months."Hyperthermia is abnormally high body temperature caused by a failure of heat regulating mechanisms.