Authorities say a bicyclist riding along the Rio Hondo bike trail near Lincoln Avenue found the remains in some bushes around 11 a.m. Detectives responded to the scene.
The remains indicate that the person had been there for some time, investigators said. The remains have not yet been identified.
The L.A. County Sheriff's Department is assisting the Montebello Police Department with the investigation.
The area is a known to have homeless encampments.