The Late Cretaceous to early Paleocene McDermott Conglomerate (~68 mya) is at the base of the Late Paleocene Animas Formation, and represents possible volcanic material derived from a early uplift to the northwest. The volcanic source of the McDermott Formation is controversial. There is no conclusive evidence for a volcanic eruption during this time. Larraine and Gonzales (2003) recently suggested that the southern margin of the La Plata Mountains laccolithic complex was oversteepened and collapsed. Material released by this collapse was then transported and deposited by debris and hyper-concentrated flows, into the San Juan Basin.