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.
[Illustration: 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)]
[Illustration: 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]
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.