[Mile-marker 39]
About a quarter of a mile from the end of the improved stretch, one may
turn right on two tire tracks, travel about a quarter of a mile farther,
and park near the junction of Rough and Ladder Canyons, where
interesting geology is reachable by short walks up Ladder Canyon or down
Rough Canyon. About a mile up Ladder Canyon is an interesting abandoned
mica mine.[42]
[Illustration: GLADE PARK FAULT VIEWED FROM THE GROUND, crossing
head of No Thoroughfare Canyon. Looking southeast from Little Park
Road just southeast of new Monument boundary. Fault passes just to
right of white cliff of Wingate Sandstone near bottom of photograph
through notch in east wall of canyon. Note that surface to right
(south) of fault has dropped about 50 feet below left side. Grand
Mesa forms skyline. (Fig. 58)]
From the left side of the road, about 9 miles northeast of our starting
point, we see the view shown in figure 60. About 2 miles farther north,
Little Park Road is paved through a suburban housing development all the
way to The Redlands; there, we may turn right, cross the Gunnison River,
and reach U.S. Highway 50; or we may turn left through Rosevale and
reach Colorado Highway 340.
[Illustration: GLADE PARK FAULT VIEWED FROM THE AIR, crossing head
of No Thoroughfare Canyon from left to right. Land south of the
fault was dropped some 50 feet below that on the north side.
Primitive road around head of canyon has been improved and realined
since photographs were taken. The stereoscopic pair of aerial
photographs may be viewed without optical aids by those accustomed
to this procedure or by use of a simple double lens stereoscope,
such as the folding ones used by the armed forces during and after
World War II. Compare with the geologic map, figure 8. Photographs
taken in 1937 by U.S. Soil Conservation Service. (Fig. 59)]
[Illustration: LADDER CREEK MONOCLINE AND REDLANDS FAULT, looking
northwest from lookout point near Little Park Road. Telephoto view
of left half of this scene is shown in figure 29; photograph of
Morrison Formation shown in figure 21 was taken from point about a
mile farther north. (Fig. 60)]
Résumé of Geologic History and Relation to Other National Parks and
Monuments in the Colorado Plateau
In the geologic story of the Monument discussed on pages 17 to 94, the
geologic processes and events leading to the Monument of today were told
in the order in which they occurred; therefore, the details of the
geologic history have already been covered. Having finished this story
and the trips through and around the Monument, let us see how the
colorful canyons, cliffs, and other erosion forms fit into the bigger
scheme of things—the geologic age and events of the Earth as a whole, as
depicted in figure 61. As shown in figure 7, the rock strata still
preserved in the Monument range in age from Proterozoic to Cretaceous,
or from about 1,500 million to 100 million years old—a span of about
1,400 million years. This seems an incredibly long time, until one
compares figures 7 and 61, and notes that the Earth is some 4,500
million years old, and that the rock pile in the Monument is only about
a third the age of the Earth as a whole.
[Illustration: GEOLOGIC TIME SPIRAL, showing the sequence, names,
and ages of the geologic periods and epochs, and the evolution of
plant and animal life on land and in the sea. The primitive animals
that evolved in the sea during the vast Archean and Proterozoic Eons
left few traces in the rocks because they had not developed hard
parts, such as shells, but hard-shell or skeletal parts became
abundant during and after the Cambrian Period. This drawing was made
when the Geological Survey and most others used the term Precambrian
to embrace what is now included in the Archean and Proterozoic Eons.
The end of the Archean Eon and beginning of the Proterozoic Eon has
been placed at about 2,500 million years ago. Also, because of more
recent radiometric dating, the ages of the boundaries between some
of the geologic periods and epochs have been changed slightly. Of
most concern to this report, the boundary between the Pliocene and
Pleistocene Epochs has been changed from 3 million to 2 million
years. Drawn by John R. Stacy originally for inclusion in a report
by Newman (1976). (Fig. 61)]