The story of Roxborough begins with the foundation – Geology. During Precambrian time, when the earth was not yet 2.5 billion years old, North America was just being formed. Sediments from the seafloor were tectonically pushed into the early continent, expanding it to include what would become Colorado. These sediments were buried, heated, and squeezed to become the various formations we see today. In the Pennsylvanian Period (300 million years ago), tectonic forces raised the Ancestral Rocky Mountains. As those mountains eroded, reddish sand and gravel was deposited by rivers draining the mountain front. This sediment became the Fountain Formation, and it forms the western line of red rock spires as well as the Flatirons of Boulder, Red Rocks Park, and the Garden of the Gods.
– Excerpt from Roxborough State Park – A Naturalists’ Guide by Tom Zeiner. Full copy available at Roxborough Visitor Center.
Formations of the Park
Photo and text credits below to Roxborough Volunteer Tom Booth
Dakota Ridge
This ridge, also known as the Hogback thanks to its resemblance to the back of a razorback hog, runs up and down most of the Front Range of the Rockies. It is made up of several different formations, which together form the Dakota Group. The ridge, formed 100 million years ago, consists of layers of sandstone, shale and limestone, deposited during fluctuations of the Cretaceous Interior Seaway, which eventually covered all of Colorado. The Cretaceous Period, which lasted from 145 million years ago to 66 million years ago, was still warm and wet and dominated by dinosaurs which left behind their tracks. However, the sea and plants also left evidence in the form of ripple marks and fossils of palms and mangroves in the rocks of Roxborough.
Morrison Formation
The grassy western hillside of Dakota Ridge is the Morrison Formation, from 150 million years ago in the late Jurassic Period. Lots of slow-moving rivers, swamps and lakes left behind a 400-foot-thick layer of soft shales and sandstones, along with ideal conditions for preserving dinosaur bones and footprints. Affectionately known in Roxborough State Park as “Jurassic Park”, the Morrison Formation was the site of the “Bone Wars” of the 1870’s when dozens of new dinosaur species were discovered near the current town of Morrison, home of Dinosaur Ridge where bones and footprints are readily visible
Lykins Formation
Named after Lykins Gulch near Longmont, this formation was created 250 million years ago during the Permian/Triassic Periods. Shallow seas created tidal flats covered with blue-green algae called cyanobacteria. The bacteria took in carbon dioxide from the atmosphere and through photosynthesis created energy for themselves and expelled oxygen which eventually made our atmosphere breathable. They excreted a sticky substance which glued together fine layers of sediment into mounds called Stromatolites. This formation is primarily red siltstone and mudstone, with a couple of thin layers of limestone, which indicates the area was covered by an ocean on at least two occasions. Large white limestone boulders are visible within Roxborough indicating the location of the Lykins Formation
Lyons Formation
Two hundred and eighty million years ago, during the Permian Period, the landscape in this area was very different than today, and resembled Great Sand Dunes National Park, in southern Colorado. Slow-moving streams and winds from the dry interior of the supercontinent Pangea deposited a layer of sand nearly 200 feet thick. Named after the town of Lyons, north of Boulder, this sandstone was used to build the buildings at the University of Colorado, as well as in the patio of Roxborough State Park. You can hike to the top of the Lyons Formation when using the Lyons Overlook trail.
Fountain Formation
Three hundred million years ago, during the Pennsylvanian Period, sand and gravel was weathered and eroded off the Ancestral Rockies, an ancient mountain range in roughly the same location as today’s Rockies. Fast moving streams carried this sediment to the foot of the mountains where they accumulated in a 1,200-foot-thick layer. Later, the sediment was cemented into sandy conglomerate, mostly by the mineral hematite, which gives the formation its reddish color. When the current Rockies formed, that layer was uplifted to the angle we see today. The Fountain Formation also makes up such iconic places including Garden of the Gods, Red Rocks Amphitheater, and the Boulder Flatirons.
Carpenter Peak
The highest point in Roxborough State Park, Carpenter Peak rises to over 7,200 feet. It is made up of both Idaho Springs Gneiss and Pikes Peak Granite. Older rocks and sediments in the Precambrian Period were subjected to intense heat and pressure deep in the earth 1.7 billion years ago and changed into a metamorphic rock called Gneiss, named after Idaho Springs where it was first described. It makes up a large portion of today’s Rocky Mountains. Six hundred million years later, granitic magma forced its way into the surrounding gneiss where it cooled and solidified below the surface. Weathering and erosion removed some of the gneiss, exposing igneous granite boulders that are atop the peak.
