Saturday, February 14, 2015

Geology of the Garden of the Gods, Colorado

At the end of January, I was fortunate to visit the Rocky Mountain Front Range, scouting an itinerary for a tour group back east. One of the highlights was a visit I made to the Garden of the Gods City Park in Colorado Springs. For years I have heard about and seen photos of this exceptional geo-scape. I was happy to finally see it in person.

A view of the entrance road off of 30th Street in Colorado Springs. The snow capped mountain in the background is Pikes Peak, elevation 14,115 ft. or 4,302 meters. As you can see the weather was fantastic during my visit, although it plays into the recurring dryness we are having here out west this winter.

Nearing the red rocks found on the main loop road. These are upturned sedimentary rocks. Pike's Peak in the background is composed of the 1.1 billion year old Pike's Peak Granite. This was intruded into the crust during the Grenville Orogeny, a mostly eastern seaboard mountain building event.

A private citizen, Charles Elliott Perkins, had bought the land that contains the Garden of the Gods and wished to make it a public park in perpetuity. His estate made sure this came to pass and it remains one of the most striking city parks anywhere - at least for the geologist and scenery seeker.

Here is a cross-section of the upturned strata along the Rocky Mountain Front Range at Garden of the Gods. In this section, the Rocky Mountain uplift would be to the left, the Great Plains to the right. Just off the section to the left is the Precambrian basement rocks. These are overlain by the Fountain Formation (here called Arkosa or arkose). The Fountain Formation is the tectonic and age equivalent of the Cutler Formation (or Group) on the Colorado Plateau. Both of these sedimentary packages resulted as outwash from the Ancestral Rocky Mountains some 300 to 250 Ma. The Lyons Sandstone provides much building rock and flagstone here in Colorado and beyond. The Morrison Formation contains numerous dinosaur fauna and the Pierre Shale is the equivalent of the Tropic and Mancos Shales on the Colorado Plateau. This is a classic section of strata!

The next series of photos are taken from a few of the paved walkways that meander through the rock formations (the "Gods").

These were once horizontal beds of the Fountain Formation but uplift during the Laramide Orogeny (70 to 40 Ma) pushed them upright. The harder conglomerate beds resist weathering and stand tall between the intervening and eroded softer shales and mudstones.

A juniper tree frames Pike's Peak.

View to the north of upturned beds of sandstone and conglomerate.

Note where the softer beds of shale and mudstone have been removed by weathering and erosion to create spaces between the fins.

The hills in the upper left are Precambrian crystalline rocks, which underlie these red beds.

A few fin tops have tumbled into the voids.

Close-up of the coarse conglomerate present in the Fountain Formation. These clasts were derived from the Precambrian bedrock that was exposed during the Ancestral Rocky Mountains uplift in the Pennsylvanian and Permian time periods. Rivers carried the debris out onto the floodplain where it became lithified into the Fountain Formation. The same scenario played out on the western side of the ancient range to become the Cutler Formation.

View to the east through a break in the fold.

History is alive here as well. Many Native tribes used the area as a well-trodden path led to a low pass in the Rocky Mountain front.

A view of Balanced Rock on the south side of the city park. Note the clasts in the conglomerate within the top bed. Balanced Rock formed as softer units were preferentially weathered out from under the tougher beds - slowly enough that the rock hasn't yet toppled.

Another view of Balanced Rock showing its precarious balancing act. Note the general dip of the beds on its pedestal. This shows that Balanced Rock has actually tilted back toward the left to maintain its upright position.

Anyone visiting Denver or Colorado Springs should pay a visit to this unique park and landscape.

3 comments:

Ariane said...

Thank you for a wonderful and enlightening post about a place that I've been visiting since 1979. So refreshing to revisit in a whole new expansive way via the keen eye of a passionate geologist! Smashing!

Kyle Swanson said...

Thanks, Wayne. This is great information. The tone and style of your writing is very pleasant, engaging, and easy to follow. I really enjoyed this page.

Kyle Swanson said...

Thanks, Wayne, for the great page. I learned a lot and found your writing engaging and enjoyable. I was a geology undergrad, so I love this stuff. I also found the cross section very informative.