Crestone Conglomerate

A Unique and Stunning Rock Only Found Locally

We welcome the Crestone Conglomerate to our Geology Time Trail at PCC.  With its fascinating geologic history, this rock can only be found in the Sangre de Cristo Mountains near Crestone (south of Poncha Springs).  It’s uniqueness is due to two unusual characteristics:  color and size of inclusions.

The distinctive pinks, purples and greens result from hematite (an iron oxide that often gives a reddish tint to rocks) seeping into the pore spaces around the rocks.  The explanation for the size of inclusions requires a bit more background.

‘Conglomerate’ simply means the rock has inclusions of various sizes (e.g. sand, pebbles, boulders); the Crestone Conglomerate has some inclusions the size of Volkswagens.

Let’s do a bit of geology, starting with mountain building in Colorado.  Remember Donovan’s song back in 1967 – “First there is a mountain, then there is no mountain, then there is.” ??  This came from a geologically correct Buddhist proverb.

Millions of years before the uplift of our current Rocky Mountains (about 70-40 million years ago), Colorado had ancient mountains called the Ancestral Rockies which were located in about the same place as today’s Rockies.  The Ancestral Rockies began to erode about 300 million years ago, as mountains do.  Terrific storms much more ferocious than anything we experience today, with enough energy to move rocks the size of cars, carried and deposited the weathered granitic material, forming the landscape we see daily.  This process has provided us with our current reddish Fountain Formation, forming some of the most well-known and beloved landscapes in Colorado today: the Garden of the Gods, Red Rocks Amphitheater, the Boulder Flatirons, and locally in Cañon City’s Red Canyon Park.  These were all deposited on the east side of the Ancestral Rocky Mountains.

The same thing was happening on the west side of the Ancestrals, and some of that eroded material ended up in what is today the Sangre de Cristo Mountains.  Both the Fountain Formation and the Sangre de Cristo Formation consist of the same eroded Ancestral Rockies material.  The Crestone Conglomerate is a member (a layer within) the Sangre de Cristo Formation.

During the time the Crestone Conglomerate layer was being deposited, huge mudslides brought down enormous boulders that would later be incorporated into the rock layer through cementation.  The Crestone Conglomerate rock layer itself was uplifted and exposed on the surface some 25 million years ago through extensive regional faulting.

Today those who wish to hike into the Sangres from either the east or west side are treated to delightfully colorful rocks along the trails.  If you’d prefer easier access to these rocks, please make your way to PCC-Fremont Campus to see first-hand the wonderful remnants of ancient geologic processes.