The Sea’s Final Retreat
Slow uplift of the Plateau, including the Monument region, caused the gradual retreat of the Mancos sea. Deposition of mud on the sea bottom gave way to deposition of beach sand, coal swamps, and then more beach sand and coal swamps. Finally, in Late Cretaceous time, the sea withdrew entirely, never again to return to the Colorado Plateau region.
Streams deposited sand, silt, and mud on the newly uplifted coastal areas. All these deposits, including some high-grade bituminous coal that was formed in the swamps, we now know as the Mesaverde Group. The thick cliff-forming sandstones of this unit are beautifully displayed in DeBeque Canyon of the Colorado River between Palisade and DeBeque, just upstream from the Grand Valley. There are several active coal mines in the Mesaverde between Palisade and Cameo, and outcrops of coal may be seen on the east side of the road just south of Cameo. The electric generating station of the Public Service Company of Colorado at Cameo is conveniently situated over a coal mine and next to the Colorado River, which supplies cooling water.
MOUNT GARFIELD, a prominent point on the Book Cliffs bordering the northeastern side of the Grand Valley. Slopes are Mancos Shale; ledge about halfway upslope is the toe of an ancient landslide deposit of Mesaverde sandstone blocks marking the level of an ancestral Grand Valley; capping beds of sandstone at crest are basal beds of Mesaverde Group. (Fig. 25)
PHOTO INDEX MAP, showing localities where most of the photographs were taken. Arrows point to distant views. Numbers refer to figure numbers. (Fig. 26)
Photographs for four figures are not shown because figures 5, 25 and 36 were taken outside the map borders and figure 1 was taken at an undisclosed locality in the monument
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The remains of dinosaurs have been discovered in rocks of this age elsewhere, but near the Monument only their tracks have been found. Some of these, in coal mines along the Book Cliffs and near Cedaredge, are 38 inches across and their placement indicates an incredible stride of 16¼ feet! Had there been highways in Mesaverde time, this bipedal giant could have crossed them in two strides.
Both the Mancos and Mesaverde once covered the Monument area but were removed long ago by erosion.