Their shock was compounded by the knowledge that police first learned about the site months ago but did little to investigate it. Some witnesses say the site was used to hold men who were abducted with the intent to force them into joining a criminal cartel -- and to teach torture techniques. 

The first of an unknown quantity of human remains have yet to be identified, but the site near the village of La Estanzuela holds at least 700 personal items, including some that appear have belonged to women and children -- such as a blue summer dress, a small pink backpack and high-heel shoes, the New York Times reports. Those and other shoes may offer one of the best indications of the potential number of people killed and/or processed at the site: There are hundreds of them. 

"The number of victims that presumably could have been buried there is enormous, and it resurfaced the nightmarish reminder that Mexico is plagued with mass graves," Mexican security analyst Eduardo Guerrero told the Times, saying what's been already uncovered is reminiscent of Nazi concentration camps. 

The volunteers' discovery of all the disturbing evidence at the small, abandoned ranch outside Mexico's second-largest city came after tips about the site's existence were left on a Facebook page run by a group of citizens who are searching for missing people, the Washington Post reports. Upon traveling to the site in western Mexico, they nudged the unlocked gate open, and soon found themselves gazing into a kind of hell. 

Their discoveries included three underground ovens -- presumably used for cremations. Using the crudest of methodologies -- poking metal rods into the dirt and then withdrawing them and smelling them -- they found human remains that included several hundred bone scorched bone shards. The tips left on their Facebook page had been confirmed: They'd discovered an "extermination camp," to use Mexican parlance.  

Eerily, the site also held several figurines of Santa Muerte. Also called "Our Lady of Holy Death" or "the Bony Lady," Santa Muerte is typically depicted as a female skeletal figure in a cape who holds a scythe in one hand and an Earth-globe in the other. Memorably depicted in Breaking Bad, the figure is viewed as something of a protector of criminal gangs, who frequently build altars to glorify her. These altars are often adorned with offerings such as cash, alcohol, and religious items. Far worse, gang members are said to sometimes offer human sacrifices. "They stole children from other towns and sacrificed them in front of her when they wanted to land a big hit," a former gang member told AFP earlier this year.