PORTLAND, Ore. (KOIN) — A human skull was found by prisoners on a cleanup crew along northbound I-5 in the Keizer area, the Oregon State Police said Wednesday night.

The Department of Corrections cleanup crew was in the area near milepost 260 around 9:20 a.m. when a small backpack was found. Authorities said the human skull — “likely that of a female in her late 30s to 40s” — was inside the backpack.

Milepost 260 is at Chemawa Road NE, not far from the Keizer Transit Center.

The skull was taken to the Oregon State Medical Examiner’s Office to work on identification. Authorities said the skull “had no identifiable features.”

No further information is available at this time. KOIN 6 News will continue to follow this story.