If you've unlocked the third island(Desert), go to Area 69. Stand about 50 feet away from it, on the northern side. Then, turn West and drive/walk until you're surrounded by large desert hills and rocks. The closest rock-type hill on your right will have a large hole beside it, with a few bodybags in it. Also, beside that, you'll see a Bobcat(truck) parked beside the hole with it's tailgate open.

Is this the work of the mafia?