With such world-famous sites
available to all, we often overlook interesting localities in our backyard
where both the causal observer and the dedicated hiker can get up close and
personal with the rocks (it’s tough to get personal with the Peak). Virtually
every Colorado Springs driver on I-25 has noticed such features as Pulpit Rock
and Austin Bluffs associated with the north-south trending highlands of the
Palmer Divide. Those driving Centennial
Blvd. and/or Vindicator Dr. are aware of the massive bluffs and upturned rocks
of Popes Bluff. But, how many people have
actually stopped to examine some of these fascinating exposures.
The hogback or Popes Bluff looking north.
The Popes Bluff Area (PBA),
including the adjacent highlands and hills of Ute Valley Park and the bluffs
associated with Popes Valley Creek (along Popes Valley Dr.), is generally
bounded by Centennial Blvd. on the west, Garden of the Gods Rd. on the south,
Rockrimmon Blvd. and Vindicator Dr. on the north and I-25 on the east. The bluffs and valley walls present numerous
well-exposed outcrops of the Cretaceous Laramie Formation including abandoned
coal mines, rock quarries, upturned hogbacks, and a large open space perfect
for hiking, bird watching, and plant identification. Jon Thorsen completed a geologic map of the
Pikeview Quadrangle (Thorson and others, 2001) and readers should consult that
publication for greater details.
Rocks of Laramie Formation dipping east at Popes Bluff.
Rocks of the Laramie Formation,
so well exposed in the PBA, represent the final regression of the vast Western
Interior Seaway (WIS) that flooded what is now Colorado during much of the
Cretaceous Period (~144 to ~65 million years ago). The oldest of the local Cretaceous rocks, and
unit representing the transgression of the WIS, are the complex of near shore
marine, beach, deltaic, and estuarine sandstones (mostly) of the Dakota
Group. These rocks may be best known as
the “Dakota Hogback”, a prominent topographic feature along much of the eastern
flank of the Colorado Front Range. The
Graneros Shale, overlying the Dakota, is dark colored shale representing
deepening waters (transgressing seas) and deposits of offshore mud. As the seaway continued to deepen, the
limestones and chalks of the Benton and Niobrara formations were
deposited. These limey muds were
followed by deposition of thousands of feet of marine muds laid down many miles
from the shoreline. This mud became
known as the Pierre Shale and is present under nearly all of eastern Colorado
(Matthews, 2003). Most of these
Cretaceous rocks described above are well exposed in or near Garden of the Gods
Park and Red Rock Canyon Park. The
Pierre Shale can readily be observed in the road cuts along Uintah Street
leading west from I-25.
Perhaps 70 million years ago
the early Rocky Mountains begin to appear and the WIS started its retreat from
Colorado. The beach sands of the
regressive seas are known as the Fox Hills Sandstone and are not well exposed
near the Bluffs; however, there is an exposure near Centennial Blvd about a
mile north of its intersection with Vindicator Dr. (see Post May 9, 2011)
Overlying the Fox Hills is the Laramie Formation, described below, while
the end of the Cretaceous, and the beginning of the Tertiary (K-T), is marked by
deposition of coarse sediments shed off the rising Rocky Mountain Front, the
Dawson Formation. One only needs to look
east of I-25 at the Palmer Divide to observe these rocks (see Post November 27,
2012).
The Laramie Formation
(description excerpted from Thorson and others, 2001) is a complex of rocks
representing rivers, beaches, channel fillings, coal swamps, flood plains,
lagoons, and estuaries---the sort of environments present along a regressing
sea. At the entrance to Popes Valley (off Rusina Road) the road cut exposes a nice
section of brownish-gray sandy shale and an organic-rick, dark-brown coaly
shale; thinner beds of fine-grained sandstones also are present. This sequence was probably deposited between
river channels. Above this section, and
well-exposed on the north side of the valley, is a thick, light gray to light
orange, crossbedded sandstone forming the valley rim (and holding up the
houses). This sandstone, and its
counterparts, represents deposition in a river system and can be seen along
Popes Bluff (from Centennial Blvd), and along the highlands and hiking trails
within Ute Valley Park.
Road cut exposing Laramie Formation along I-25 at entrance of Popes Valley Drive.
One of the more fascinating
sections of the Laramie Formation can be observed where Vindicator Dr. cuts
through a hogback near Centennial Blvd. (by the vehicle driver), or at the
western edge of Ute Valley Park (by the hiker).
At this locality forces associated with the rising Rocky Mountains have
turned the Laramie Formation up to near vertical and a prominent hogback, held
up by resistant channel sandstones, forms a spectacular topographic feature. Along most of the hogback the beds are
dipping to the east about 60 degrees.
Near vertical beds of hogback (also associated with faulting).
Road cut along Vindicator Drive, a cut through the hogback.
During the late 1900’s and
early 20th century, the mining of coal was somewhat of a major
industry in and near Colorado Springs. A
number of coal mines operated in the PBA although I have been unable to locate
much solid data on production. Thorson
and others (2001) produced a map showing perhaps a dozen known mines in the
PBA. Several old, but caved in, adits
are visible along Popes Valley Dr. and in the adjacent stream valley to the
north. A very visible mine dump is
easily seen about 1000 yards south of the Vindicator Dr.– Centennial Blvd.
intersection. The last mine to shut down
in the PBA was the Pikeview Mine (total production of 8,738,174 tons) in 1957
and located off Delmonico Dr. immediately north of Rockrimmon Blvd (Thorson and
others, 2001). Also of interest is the
fact that an oil well was drilled in the highlands near the mouth of Popes
Valley. The Rusina Ranch No. 1, spudded
in 1959, was abandoned at a depth of 485 feet.
I was unable to locate information about a possible pay zone but perhaps
operators were aiming for a sand zone in the Pierre Shale. At any rate, the well was abandoned early.
Abandoned coal mine near Vindicator Drive.
Although fossils, including
plants, dinosaurs, fish, turtles, amphibians, and mammals have been found at a
number of Colorado localities, I am unaware of “good” body fossils in the
PBA. The carbonaceous shales of the
Laramie Formation contain plant fragments and many sandstones contain macerated
bones and plants; petrified wood (non-gemmy) is common. Johnson (2002) noted that hard-to-identify
dinosaur tracks are present in the area.
What the observer will notice, however, are numerous pseudofossils (such
as nodules, concretions, and differential weathering), animal burrows, and
sedimentary structures.
Ute Valley Park may be
accessed from a parking lot off Vindicator Dr. or from a trailhead off upper
Popes Valley Dr. The best way to observe
the geology is to take a stroll in the Park.
One never knows what interesting features will show up.
SOURCES CITED
Johnson, K.R. Ancient
Denvers. 2002.
Matthews, V., Lynn, K.K, and
Fox, B., editors. Messages in Stone:
Colorado’s Colorful Geology. Denver:
Colorado Geological Survey, 2003.
Thorson, J.P., Carroll, C.J.
and Morgan, M.L. Geologic Map of the Pikeview Quadrangle, El Paso County,
Colorado. Denver: Colorado Geological Survey, Open-File Map and Report
01-3, 2001.
