MEXICO CITY (AP) — Volunteer searchers found 12 skeletons and one decomposed body in a shallow pit in the desert near the Mexican resort of Puerto Peñasco.

Prosecutors in the northern border state of Sonora said late Thursday that two of the bodies may be women. Tests are being conducted to determine the gender and identity of the bodies.

Prosecutors said only one of the bodies was relatively recent; the others were “complete skeletons with clothing.”

The bodies were found by a group of women known as the Searchers of Puerto Peñasco. The group is made up of relatives of missing people who investigate reports of clandestine burial sites.

Because of deficient police investigations, such volunteer groups have been responsible for discovering mass graves and burial pits in many parts of Mexico.

Drug and kidnapping gangs use such pits to dispose of the bodies of victims or rivals.

Puerto Peñasco is also known as Rocky Point. It is located on the Gulf of California, also known as the Sea of Cortez.

While not as violent as some other parts of Mexico, Puerto Peñasco has been known for Sinaloa drug cartel activity and a large-scale shootout between cartel gunmen and military forces occurred there in 2013.