A group of mothers in Mexico uncovered a mass grave with the remains of at least 42 bodies near the resort town of Puerto Peñasco, south of the Arizona border, officials said Saturday.

The group, known as the Madres Buscadoras de Sonora – or Searching Mothers of Sonora – investigates reports of clandestine burial sites to find missing loved ones and bring closure to their families. The group is made up of relatives of missing people.

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“I take comfort in knowing that families are going to be united with their loved one...and that they will have a proper burial, like they deserve,” Ceci Patricia Flores, the group’s founder and mother of two missing boys, told KGUN-TV in Spanish.

The searchers made the grisly discovery Thursday, finding 12 "complete skeletons with clothing” and one decomposing body in a shallow pit in the desert along the Gulf of California, also known as the Sea of Cortez, prosecutors told The Associated Press.

On Friday, the body count rose to 27, and by Saturday the total tally reached 42, Lupita Orduño, a spokeswoman for the Sonora Attorney General's Office, told the Arizona Republic. It was unclear how long the remains had been buried.

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Two of the bodies were still in a state of decomposition, likely indicating they were buried recently, the state said. A majority of the remains were skeletal. While tests are being conducted to determine the gender and identity of the bodies, at least two may be women based on their clothing.

Orduño told the Republic that it is too early to speculate on why the bodies were buried in the mass grave. Investigators are working to determine how they died.

Poor police investigations have led to the formation of such volunteer groups and their subsequent discoveries of mass graves and burial pits in many parts of Mexico. Drug and kidnapping gangs are known to use the pits to dispose of the bodies of victims or rivals.

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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.

Puerto Peñasco, commonly known as Rocky Point in Arizona, is about a three-hour drive southwest of Phoenix.

The Associated Press contributed to this report.