Perhaps the most well resolved basin in the Rocky Mountains, the Denver basin marks an influx of conglomerate material, with the Arapahoe conglomeratic at the base of the D1 sequence, dated at 68 mya. Clastic sediment continued along the east flank of the Front Range of the Rocky Mountains until around 64 mya. A second sequence of sedimentation dated to around 54.3 mya overlays the earlier rocks, representing an unconformity during the late Paleocene (Raynolds & Johnson, 2003;Soister & Tschudy, 1978).