The hikers discovered the bones in an isolated area off of Morrison Canyon Road, Fremont police spokesman Detective Bill Veteran said.
The purpose of today's search is to try to find additional bones that might match those found over the weekend, he said.
The bones appear to have been in the area for one to two years, Veteran said. He said they appear to be the bones of an adult.
Fremont police are conducting the search along with Fremont firefighters and members of the Alameda County Sheriff's Office.
Morrison Canyon Road will be closed indefinitely from Canyon Heights Drive to Vargas Road, Veteran said. Residents will still be allowed in, he said.