There's no way to tell the age of bones recently discovered in the hills near Pleasanton, according to a spokesman from the Alameda County Sheriff's Office.
"They've been there a while," said Sgt. J.D. Nelson.
"There's no outward appearance of foul play," he added, and for now, homicide investigators are looking over missing persons reports from the area.
A hiker stumbled upon what appeared to be a human skull Sunday in the area near the 11000 block of Dublin Canyon Road. Deputies called to the scene agreed it was a skull and located additional bones nearby.
Investigators are also looking into the possibility that the bones - believed to be those of a man - are from a transient.