A rider suffered critical injuries Saturday at the Lucas Oil Motocross Park, officials said.
The man's heart had stopped beating by the time medics arrived at the scene of the rider down, reported about 9:30 a.m., Cal Fire's Melody Hendrickson reported.
It occurred at 18700 Lake Perris Drive, according to Cal Fire.
The Riverside County Coroner's office had not been called about the case as of Saturday afternoon, an investigator told Patch.
Medics took the rider to an area hospital, Hendrickson said.
The incident was under investigation, Hendrickson said.