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Roxborough State Park – Front Range Colorado Gem

October 14, 2020


Roxborough’s 300-million-year-old red sandstone Fountain Formations that tilt at a 60 degree angle

From our home in Northwest Denver, Roxborough State Park is some 35 miles away, south past the Chatfield Dam and onto North Rampart Road. When I first came to Colorado 51 years past, there was “nothing” out there, that is to say a few ranches along the edge of the mountains reaching out onto the High Plains. Now it’s a different story with the development cancer extending to the edge of the park. That the park itself didn’t get gobbled up in some development scheme is about as close to a miracle that I can think of. Visiting Roxborough anytime of year is worth the effort, but to do so on a mild and sunny day in early October with the trees and bushes turning different shades of green, brown, yellow and red only adds to the experience.

There must be a story behind its preservation that I’ll unearth one day. Whatever, it is, among the state’s natural wonders, or what hasn’t been developed, mined, fracked or nuclear bombed (Project Rulison, Rio Blanco), radiated for milleneum’s to come (Rocky Flats) or otherwise poisoned by unchecked development or breathtakingly stupid or dangerous federal projects (Rocky Flats, Rocky Mountain Arsenal)as of yet.

It takes close to an hour to get there, a fact which has discouraged us from spending more time at Roxborough then we have. Last time we had hiked this park, I got some decent shots of a spotted towhee. Hoping to repeat that, or find another bird not common in northwest Denver, I brought my monster lens (150-600 mm), but on that score came up short as we saw very few birds of any variety, and those we did see were too far away to photograph. A group of 4-5 Stellar Jays crossed our path at a distance and a circling red-tailed hawk looked promising. Took a dozen of it but only one or two were not blurry. That”s how it goes photographing brids. Sometimes you win (rarely), sometimes you lose (mostly) but the fact that the photos are digital and not film based, softens the blow. Anyhow, frustration and disappointment come with the hobby

Birds might have been scarce but the geological history of the place – if you follow the guide book or have a basic knowledge of the place – makes up for it.

In fact, this past Friday was only our second visit to the place, the first coming two years ago in April, then as now, with David Fey, Nancy’s younger brother. Certainly it isn’t necessary to have a lifelong geo-chemist along to enjoy the place, but going there in David’s company greatly enriches the experience as it is nothing short of a geological wonder in its own right. It puts the history of the earth and its evolution in a broad perspective, a starting point for deeper study, and freeing the mind from the idiocy of fundamentalist religious explanations of the history of the earth.

It’s one thing to look at rock formations and vaguely understand that they originate from different moments in the earth’s rich 4.5 billion year history. It’s quite another to understand the sequence of the formations and approximate dates that they burst forth from under the earth. The most dramatic geological formations there  from the Pennsylvanian epoch of the Fountain Formation- the red sandstone near vertical structures – Colorado’s classic “red rocks” – are what remains of  the 300 million (300, 000, 000 mya) year old “Ancient Rockies.

Geological uplifting – the submersion of one tectonic plate under another – to push up surface formations – causes the rocks, as in the photo above to appear near vertical, their tips facing east. Roxborough’s 300-million-year-old red sandstone Fountain Formations that tilt at a 60 degree angle. On the other side of the Rockies, in Utah, similar formations face west. This formation, also found at the Garden of the Gods and the Red Rocks amphitheater, is a completely different range from the modern Rockies which emerged only some sixty million years ago. As the Ancient Rockies rose over time, as the Roxborough State Park websited notes. “they began to erode into large sheets of sediment, producing the oldest sedimentary rocks seen in the park. The mountains continued to erode until the region became relatively flat. This ancient flat surface still remains on top of some fourteeners today.”

Roxborough Geologic Section Picture

For as old as are the Ancient Rockies, there are granite formations that date from even earlier geological eras, some as old as two billion years (2,000,000,000 ya) although they are not as obvious. As the photo image below shows, there are other formations that anyone hiking and walking the trails at Roxborough can discern without much difficulty.  Somewhat later than the red rocks of the Fountain/Pennsylvanian formation is a layer of largely buff and pink material known as the Lyons formation. A bit younger than the Ancient Rockies at around 250 million years. formed during the Paleozoic Era,. It is the result of fine-grained quartz sand dunes compressing into sandstone.

This layer is visble along the Front Range of the Colorado Rockies. The stone quarried from this layer (Lyons formation) was used to build many buildings on the University of Colorado – Boulder campus. During the time of the Lyons formation, Roxborough was the western shore of a broad sea that intermittently covered an area of low relief, where sediments, including the Lyons, were deposited in environments ranging from fluvial (river and stream flows) to normal marine to hypersaline (with high salt content) environments. Oil is trapped in the Lyons formation and is drilled elsewhere in Colorado. Although there is no drilling at Roxborough, at Keota, in the northeast corner of the state oil production in this layer began in 1953; at present there are five other fields with a total oi production of more than 12 million barrels.

Still younger yet, at the eastern boundary of Roxborough Dakota formation hogback rises as a result of uplifting. It is primarily composed of beach and near shore sediments “laid down on the wester shoreline of a seaway that began to flood the center of the North American continent around 100 million years ago. Dakota formation outcrops are widespread, producing colorful rock formations. The formation is known for its dinosaur footprints and early deciduous tree leaves. Dinosaur Ridge with its well-known and frequently visited dinosaur footprint viewing area west of Denver is another example of the Dakota formation. The sandstone of this formation holds within its boundaries the Dakota Aquifer, one of the important sources of water on the increasingly arid Great Plains. Also, Dakota formations are made up largely of shales and mudstones, a source of oil and gas drilling throughout the Denver Basin.

More to follow after our next visit…

Dakota Hogback at Roxborough looking east to the south Denver suburban sprawl

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