The Fresno County Sheriff's Office said the plane wreckage was spotted near Red Lake, about five miles southeast of Huntington Lake. They said the elevation at the site was approximately 9,000 feet.
Ian Gregor, public affairs manager for the Federal Aviation Administration, said search crews found the wreckage and reported seeing the pilot walking outside the aircraft. He said the condition of the pilot is unknown at this time.
The pilot was the only person on board the plane, according to Gregor.
Gregor said the pilot of the Piper PA28 radioed Fresno air traffic control around 10 a.m. on Thursday morning that he had low oil pressure and he was going down in the Sierra.
The FAA and NTSB will be investigating the accident.