|Arch in Laramie Formation, Ute Valley Park.|
The Colorado Springs area is home to some of the world’s most fascinating geological wonders ranging from Pikes Peak (igneous rocks, mostly granitic, emplaced about 1.1 billion years ago) to majestic ridge- and spire-forming sandstones of late Paleozoic age (~325-290 million years ago) cropping out in Garden of the Gods Park. Unlike many other “famous” localities, the areas of geological interest in and near Colorado Springs are readily assessable to most people. The rocks of majestic Pikes Peak may be observed along the Pikes Peak Toll Highway, US Highway 24 to Woodland Park, as well as along numerous secondary roads such as the Old Stagecoach and Gold Camp roads leading to Cripple Creek. Garden of the Gods is a Colorado Springs city park readily accessed by several roads and trails.
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.
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.
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.