Dinosaurs on the Move
The wet climate of Late Jurassic time was followed by arid or semiarid climate in the Early Cretaceous. Streams continued to deposit gravel, sand, silt, and mud, but at a much slower rate. These deposits eventually hardened into the conglomerate, sandstone, and green shale or siltstone of the Burro Canyon Formation. This formation, together with part of the overlying Dakota Sandstone, caps Black Ridge, the highest part of the Monument (7,000 feet) about a mile west of the Coke Ovens. Several airway beacons on this high ridge may be seen for many miles. The Burro Canyon is best seen below the Monument on the west side of Monument Road along the lower part of No Thoroughfare Canyon, where it is about 60 feet thick ([fig. 24]).
BURRO CANYON FORMATION AND DAKOTA SANDSTONE, along west side of No Thoroughfare Canyon, about 2½ miles northeast of the Monument’s East Entrance. Basal sandstone above road and unexposed green shale (brown in photograph) comprise the Burro Canyon, here 58 feet thick. White band two-thirds the way up the slope is 40-foot basal conglomerate of the Dakota Sandstone, above which is 58 feet of carbonaceous shale, a 14-foot bed of sandstone, and 17 feet of sandy shale to the top of the hill. The top of the Dakota has been eroded away. (Fig. 24)
A few fossil plants and shells have come from the Burro Canyon Formation, but the seeming absence of dinosaur bones suggests that possibly these reptiles had to move to areas of greater precipitation, where food was more abundant. Some dinosaurs may have lived in the area at this time, but their bones either were not fossilized or they have not yet been found.