The grave is a large hole dug approximately 6-12 feet deep in the ground at the base of a large Mesa formation in the Northern Bone County desert. A Bobcat pickup truck sits in front of the hole in a position implying the bodies were previously loaded into the tray and brought to the location, before the suspects were interrupted and abandoned the vehicle in haste or simply left it behind.
Colonel Henry Bolt
According to the Grand Theft Auto: San Andreas website, Henry Bolt was the colonel of the 66th Cavalry stationed in Fort Carson who, in 1862, led his unit on an attempted attack on Las Barrancas. Unfortunately, the Colonel and his entire squad fell into a hole before they reached the settlement. The Las Barrancas Mass Grave stands as a tribute to their service and in memory of Bolt's forces.
Despite not having a known physical presence in the game, some players linked the mention of the Las Barrancas Mass Grave with the one found in El Castillo del Diablo. However, some discrepancies surface over the location of the graves.
The article states the Colonel attempted to lead the force from Fort Carson to Las Barrancas, when, considering the location of the Mass Grave in El Castillo del Diablo, it would seem he was leading them toward Las Payasadas or El Quebrados.
Furthermore, it cannot be assumed the Sherman Dam was complete at the time nor that there was a bridge linking Las Payasadas and El Quebrados. So, if the Colonel was attempting a flanking maneuver and planning to attack Las Barrancas from the North, he would have had to lead his force past two assumed enemy settlements.
This suggests one of three possibilities. The Mass Grave could have been located near the town of Las Barrancas in the Beta version of the game. Or perhaps Las Barrancas and Las Payasadas had a name switch somewhere between the Beta version and the final release. Or, as some players have suggested, the story of Colonel Colt was fabricated for tourists, and the Mass Grave of El Castillo del Diablo was dug long after those events and serves a more macabre purpose; the disposal of corpses of recently murdered humans.
Mr. Trenchcoat has long been believed to be the person responsible for the Mass grave. Players theorize he lives in a small house on a dirt track just off the main road running South between El Quebrados and Las Barrancas and regularly kills other Pedestrians, dumping their bodies in the Grave. They go on to link the type of vehicle that spawns near his suspected place of residence with the one that appears at the Mass Grave, however, this piece of evidence is incorrect as the vehicle that spawns near the house is a Sadler, not a Bobcat.
Despite being labeled a Serial Killer, Mr. Trenchcoat is most likely someone suffering from alcoholism possibly brought on by trauma as a result of an extraterrestrial encounter of the fourth kind.
Players have theorized the grave is a body dumping ground for mafia families. A major piece of evidence to this theory can be seen in the game’s Introduction video where Two Sindacco Family Gangsters can be seen digging a grave. However, they are shown attempting to dispose of only one corpse and the exact location the thugs were shown to be digging has been proven to be elsewhere in Bone County.
Another suspect myth hunters have theorized to be responsible is Mary-Beth Maybell, the host of the radio station K-Rose. During one of her broadcasts, she says that she has six husbands, all of which are now “six feet under”. Players were quick to link her number of husbands to the number of body bags in the Mass Grave. Mary-Beth also announces that she broadcasts from somewhere in Bone County, placing her in close proximity to the grave. At one point in her show, she also reveals she drives a truck, which players have theorized to be the Bobcat near the grave.
Giorgio Forelli, a Capo of Vice City's Forelli Family, has also been suggested to have been responsible for the Grave. Player's theorize his presence in San Andreas could be explained by assuming he traveled with his lawyer, Ken Rosenberg, when Ken moved to Fort Carson Medical Center for Rehabilitation. Players cite his suspected involvement in the Car Grave Myth and his involvement in the Forelli Family as evidence. The Family's practices are particularly brutal, as seen in the proven Forelli Family Barbarity Myth. Theory with some evidences.
Players have also linked the site with operations at the nearby Area 69 military installation, theorizing that guards have disposed of intruder’s corpses. This however is unlikely as a government run military installation would possess the foresight to incinerate bodies. Others suggest the facility is disposing of alien corpses or experiments in the grave, this however is even more improbable as the facility would likely freeze extraterrestrial corpses for later study and incinerate dangerous or infected tissues.
Further speculation proposes a Grave Robber has disposed of excavated corpses in the grave. Exactly which graveyard has been defiled is a mystery, but interestingly, there are six graves in the nearby Las Brujas cemetery and six body bags in the Mass Grave.
Perhaps the most outlandish of all, some believe the Mass Grave is the work of The Creeper, the antagonist of the Jeepers Creepers movies. The existence of The Creeper in San Andreas is currently listed as False and the only piece of evidence linking him to the Mass Grave is that in the movies he places his victims in body bags.
It is most likely the Mass Grave is an Easter Egg by Rockstar intended to reference real-life mafias from Las Vegas who disposed of the bodies of their enemies in the city’s surrounding deserts.