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Geological Survey Bulletin 1508
The Geologic Story of Colorado National Monument
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TRIPS THROUGH AND AROUND
THE MONUMENT29
29In the following sections the small numbered
triangles in the right margin refer to key points along the trip routes.
Figure 3 shows the locations
of these key points. These numbers should be especially helpful if the reader
happens to follow the road guides in reverse.
From Grand Junction through the
Badlands to the West Entrance of the Monument
1 STARTING POINT |
WE WILL BEGIN OUR TRIP in the southwestern part of
Grand Junction at the intersection of First Street and Grand
Avenue, (this is also the intersection of U.S. Highways 6 and
50 and Colorado Highway 340), by following a sign on
Highway 340 pointing westward toward the Monument. After crossing a
viaduct over the railroad yards and a bridge across the Colorado River,
we come to a traffic light and a sign pointing left toward the
Monument. The road to the left connects with Monument Road which leads
up No Thoroughfare Canyon to the East Entrance. However, we will
continue westward toward The Redlands.
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2 REDLANDS CANAL |
Just beyond the stoplight we cross a bridge
over the Redlands Power Canal which carries 675 cubic feet per
second (cfs, or ft3s-1)30 from
the Redlands Diversion Dam on the Gunnison River about 2-1/2
miles south of Grand Junction. A quarter of a mile northwest of
the bridge, most of the water falls to a lower powerplant that
generates electricity for pumping the remaining 50 cfs to three
lift canals, which are used mainly for irrigating peach orchards
in the eastern part of The Redlands.
30One cfs. or one
ft3s-1, = 448.8 gallons a minute or 2446.6
cubic meters a day.
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3 SOUTH BROADWAY |
After Colorado Highway 340 curves right it is known
as Broadwaya paved road serving much of The Redlands and
connecting with the West Entrance of the Monument. We will follow
Broadway about 3 miles, passing low outcrops and roadcuts of the
Dakota Sandstone, some of which contain coal beds and some of which are
covered by a veneer of gravel laid down by the river when the channel
was higher. Then, at the first store and filling station we turn
southwest on another paved road known as South Broadway.
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4 SOUTH CAMP ROAD SIDE TRIP |
Just around the curve to the right is a
T-intersection from which paved South Camp Road leads south to a growing
suburban area; and 2-1/2 miles to the southeast it connects with Monument
Road at a point only half a mile north of the East Entrance of the
Monument.
Excellent views of the cliffs of dark Proterozoic
rocks, the overlying cliffs of the Wingate Sandstone, and the Redlands
fault along the northeastern border of the Monument are seen all along
South Broadway, but views from South Camp Road and several connecting
roads to the southwest are especially good. (See figs. 37 and 38.) As
noted earlier, the Redlands fault has a maximum vertical displacement of
700 or 800 feet, but dies out in scissors fashion at each end.
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REDLANDS FAULT, looking west from South Camp Road
about one mile south of South Broadway. Fault here is nearly vertical
and normal, and lies between updragged Wingate Sandstone and dark
Proterozoic schist, gneiss. and granite. All or most of the soft Chinle
Formation has been squeezed out along the fault. Note smooth erosion
surface atop hard, dark rocks surmounted by slope of red Chinle
Formation and cliffs of Wingate Sandstone capped by lowermost resistant
beds of Kayenta Formation. (Fig. 37)
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CLOSEUP OF UPDRAGGED WINGATE SANDSTONE ALONG
REDLANDS FAULT, looking northwest from side road 1-1/2 miles
southwest of intersection of South Camp Road and South Broadway. White
"pimple" atop cliff near left skyline is Liberty Cap, an erosional
remnant of the Wingate Sandstone, reachable via the Liberty Cap Trail
(fig. 3; and p. 108). Chinle Formation here was largely squeezed out
along the fault. (Fig. 38)
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5 BRACHIOSAURUS MONUMENT |
As we continue westward on South Broadway, note on
right the brightly colored mudstone and siltstone of
the Brushy Basin Member of the Morrison Formation strewn with large
blocks of rusty-looking sandstone from the Burro Canyon Formation, which
caps the high ridge on the right. Just above the deep cut on the right
four-tenths of a mile west of the intersection with South
Camp Road is a bronze plaque set in a masonry monument, whose lettering is easily readable
in figure 39. Many years after the excavation in 1900 (fig. 22), Elmer
Riggs contacted Al Look, of Grand Junction, in regard to the casting and
erection of this plaque. Al, Elmer, Ed Faber, and a few other citizens
put up the necessary funds and personally erected the plaque and
monument. Somehow or other, Brachiosaurus was misspelled
Brachyosaurus, as shown in figure 39, but the intentions were
good. Later I will call attention to another similar monument
commemorating the finding by Riggs of another dinosaur skeleton.
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BRONZE PLAQUE AND MONUMENT MARKING THE DISCOVERY
OF BRACHIOSAURUS ALTITHORAX RIGGS, above roadcut on South Broadway
four-tenths of a mile west of South Camp Road. See also figure 22. For
discrepancy in spelling text. (Fig. 39)
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WATCH TURNS |
After a sharp turn to the north and another to
the west, South Broadway reaches the top of a hill just above the
Elk's Club and curves gently to the right past sandstone
lenses in the Salt Wash Member of the Morrison Formation. A 610-foot-deep
well at the house on the left formerly flowed
about 1-1/2 gallons a minute from the Entrada and Wingate Sandstones.
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6 LEFT TURN WATCH FOR BUFFALO |
Half a mile to the north, South Broadway
turns sharply to the left even though another paved road continues
northward. Three-fourths of a mile to the west, we turn
northwestward parallel to the Monument boundary fence for seven-tenths of a
mile before turning north again. The 7-foot
chain-link fence just to the left of the road is the northeastern
boundary of the Monument and encloses the herd of buffalo. In the late
forties or early fifties a young bull challenged the older leader for
possession of the herd and gored and pounded the old bull so badly he
had to be shot by a ranger. During the furious battle 125 feet of this
strong steel fence was utterly demolished. It is reported that sometimes
an old bull simply takes one look at the young challenger and retreats
without a battle, but other lone or rogue bulls may temporarily or
permanently leave the herd for other reasons. Such outcasts are
dangerous and unpredictable. One bull kept a ranger "treed" for 4 hours
on a steep rock ledge in the broiling sun before moving on to a
patch of grass. Four of these critters delayed by one week my walking out
a stretch of the Redlands fault on their side of the
fence. I decided that a live geologist had advantages over a
dead hero.
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REDLANDS FAULT 7 WINGATE DRIVE SIDE TRIP |
Throughout most of its 6-mile length the Redlands fault is
a vertical or nearly vertical normal fault, but along and near
this 0.7-mile stretch it is a reverse fault that dips from 45° to 60°
to the southwest, as shown in figure 40 and in the cross section of
figure 8. Good views of the fault are seen all along the fence,
but especially at points one-tenth and four-tenths of a mile
northwest of the first turn, the second of which is shown in
figure 40. Just after turning north on South Broadway, let
us turn west a few hundred feet on paved Wingate Drive to see
the northwest end of the Redlands fault, which passes
through a col to the left of updragged remnants of the thinned red
Chinle Formation and the Wingate Sandstone, as shown in figure 41.
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REVERSE PART OF REDLANDS FAULT, looking N. 65°W.
from point on South Broadway along boundary fence. Most of Chinle
Formation has been squeezed out, but lower part of Wingate Sandstone may
be seen dipping about 45° southwestward beneath dark Proterozoic
rocks. Next pink band to right is Entrada Sandstone. Jumbled mass of
white sandstone slabs at right of photograph is part of Salt Wash Member
of Morrison Formation and is known locally as "White Rock". (Fig.
40)
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NORTHWEST END OF REDLANDS FAULT, passing through col left of
updragged remnants of Chinle Formation and Wingate Sandstone. Fault, which here
is normal, ends against unbroken Lizard Canyon moncline in next canyon
to northwest. Looking west from point just south of Wingate Drive a
few hundred feet west of South Broadway. (Fig. 41)
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MONUMENT CANYON TRAIL |
About half a mile north of the last turn, South
Broadway rejoins Broadway (Colo. Highway 340) at a stop sign. After
we turn left on Broadway and reach the first curve, we get a nice
view westward into Monument Canyon, as shown in figure 42.
The Park Service hopes to establish a new trailhead at the
bridge one-tenth of a mile west of the curve, from which a new
section of trail will follow the normally dry wash southwestward
to join the old Monument Canyon Trail. After we cross
the creek leaving the canyon, we pass a low hill of
the Salt Wash Member of the Morrison Formation on the left. Just beyond
the hill, the dirt road leading southwest to a farmhouse formerly was
the beginning of the Monument Canyon Trail (fig. 3). There is a new
temporary trailhead a quarter of a mile north, but it is hoped that a
permanent one can be built at the bridge about a quarter of a mile to
the southeast, as noted above. Hikers may see buffalo along this trail
and should watch out for outcast bulls.
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LOOKING WEST INTO MONUMENT CANYON, from curve on
Broadway just northwest of end of South Broadway, showing Independence
Monument. This monument was seen in figure 6 and will be seen again in
figure 51. Redlands fault ends in this canyon; Lizard Canyon monocline
can be seen on extreme right. (Fig. 42)
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8 DRAINAGE DIVIDE |
About half a mile north of the farm road we
reach the highest point on Broadway (Colo. 340) at a drainage
divide. Inasmuch as the three Redlands Lift Canals end east of the
divide, there is quite a contrast between the lush irrigated lands east
of the divide and the nearly barren desert to the west, a view of
which is shown in figure 43. To the southwest of the divide
is an excellent view of the northeastward-dipping beds on the Lizard
Canyon monocline. On the left about a mile northwest of the divide we
pass the other entrance of Monument Canyon, then Lizard Canyon, and a
switchback on Rim Rock Drive ascending the ridge between Lizard and
Fruita Canyons. The water well beneath elevated tank on left is 650 feet
deep and formerly flowed at about half a gallon a minute from the
Wingate Sandstone. Household needs are obtained by pumping.
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LOOKING WEST FROM DIVIDE ON BROADWAY 2 MILES EAST OF
WEST ENTRANCE TO MONUMENT. Monoclinal hill on right is Brushy Basin
Member of Morrison Formation capped by basal beds of Burro Canyon
Formation. Rocks at left middle are blocks of sandstone in the Salt Wash
Member of the Morrison. (Fig. 43)
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ROAD INTERSECTION |
At the next intersection, Colorado Highway 340 turns
right and continues about 2-1/2 miles to Fruita; the highway to the left
reaches the West Entrance of the Monument in a quarter of a mile. Before
turning left into the Monument, however, we will interrupt our
description of the trip by making a new start from Fruita for the
benefit of people travelling from this direction.
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bul/1508/sec12.htm
Last Updated: 8-Jan-2007
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