A group of Mexican volunteers found the remains of at least 13 people in shallow pits in the desert near the Mexican beach resort town of Puerto Peñasco, also known as Rocky Point.
The volunteers made the discovery on Thursday along a state highway east of Puerto Peñasco, the Sonora Attorney General’s Office confirmed, according to reports.
Sonora is a Mexican state that shares the U.S.-Mexico border mainly with Arizona. State officials say more bodies could be recovered as they continue their search of the area, the Arizona Republic reported.
The bodies were fully clothed. The identities of the remains are unknown, and it is unclear how long they have been buried.
Prosecutors in Sonora noted that one of the 13 bodies was relatively recent, while the rest were “complete skeletons with clothing,” reported The Associated Press. Prosecutors also said late Thursday that tests so far suggest at least two of the bodies may be women.
“We’re just now trying to identify the cause of death,” Lupita Orduño, the spokeswoman for the state’s Attorney General’s Office, told the Arizona Republic. “We don’t know how they were killed. And that’s what the forensic lab will do.”
In a statement seen by the outlet, the state agency said, “The Attorney General’s Office, which has been joining the collective of women searching, recovered the remains for transportation and their eventual analysis that will allow for the identification of these deceased persons.”
The volunteers who found the bodies are part of the group “Madres Buscadoras de Sonora,” translated as the “Searching Mothers of Sonora,” which comprise relatives of missing people who investigate reports of clandestine burial sites.
On their Facebook page, they describe themselves as “mothers searching for missing persons or human remains, to bring peace to other families that are going through the same pain.” Photos posted to their page on Thursday show women and forensic workers digging up the pits in the secluded desert area.
Because of deficient police investigations, such volunteer groups have been responsible for discovering mass graves and burial pits in many parts of Mexico, according to The Associated Press.
The news agency noted that drug and kidnapping gangs often use such pits to dispose of the bodies of their victims or rivals.
Puerto Peñasco is located on the Gulf of California, also known as the Sea of Cortez.
The city has been known to witness drug cartel activity from the Sinaloa Cartel. The city also saw a large-scale shootout in 2013 between the cartel and military forces.
The Associated Press contributed to this report.