NEAR JOINT BASE LEWIS-MCCHORD, Wash. -- Investigators are trying to identify a skull found by a passerby on Wednesday afternoon.

Officials said a civilian who had stumbled onto the base found the skull near the east gate at approximately 1 p.m. 

Investigators said they've not made any determination about the found bone, and are combing the area for additional clues. The area has been cordoned off. 

"We're treating this as a possible crime scene," said base spokesman Joseph Piek. 

Officials said because the base, which borders the Nisqually Indian Reservation, houses ancient burial grounds, it is common to find remains in the area. However, they added the skull doesn't appear to be old enough to have surfaced from the burial grounds. 

"Right now, don't know what we've got," said Piek. 

Before they begin reviewing missing persons cases that could be a match, investigators want to make sure they've gathered every piece of evidence. For the time being, the investigation is staying on base.