The Garden of the Gods is a National Natural Landmark in Colorado Springs, Colorado, known for its striking landscape of towering red rock formations. This park showcases a geologic history spanning over a billion years. The spires and fins visible today resulted from immense environmental changes, including ancient seas, deserts, and continent-shaping tectonic forces. The park’s formation involved the deposition of sediments in horizontal layers, followed by powerful uplift and relentless erosion that sculpted the raw materials into the spectacular scenery visitors enjoy today.
The Foundation: Ancient Seas and Sediment Deposition
The foundation of the region is ancient crystalline rock, primarily the Pikes Peak granite, which solidified from magma over a billion years ago. This hard, Proterozoic-era granite forms the core of the mountain range to the west and served as the source material for later sedimentary layers.
Beginning about 300 million years ago, the erosion of the Ancestral Rocky Mountains deposited vast quantities of sand, gravel, and mud onto this granite base. These sediments were carried by ancient rivers and streams, compacting into the thick, coarse-grained rock layers of the Fountain Formation.
The environment later shifted to a vast, arid desert during the Permian period. Powerful winds swept fine-grained sand across the landscape, creating massive dune fields. These wind-blown sands were buried and cemented into the Lyons Sandstone. Subsequent periods saw the land covered by shallow marine environments, such as the Cretaceous Seaway. These invasions deposited additional horizontal layers of fine muds, shales, and limestones on top of the older sandstones.
The Tectonic Force: Uplift and Tilting of Rock Layers
The horizontal stacking of these sedimentary layers was interrupted by the Laramide Orogeny, a mountain-building event that began about 70 million years ago. This tectonic episode created the modern Rocky Mountains through the shallow-angle subduction of an oceanic plate. The immense pressure caused the crust to buckle and fracture, pushing large blocks of the Pikes Peak granite core upward.
This uplift forced the sedimentary rocks draped over the granite core to fracture and deform along major fault lines. The Rampart Range Fault accommodated much of this displacement. As the rigid granite block rose, the surrounding, more flexible sedimentary layers were bent and thrust upward along the fault’s edge. This intense compression tilted the once-flat layers of sandstone and conglomerate into their current, near-vertical positions.
In many areas, the rock beds now stand at angles approaching 90 degrees, sometimes slightly overturned. This dramatic faulting exposed hundreds of millions of years of geological history. The layers nearest the rising Pikes Peak massif experienced the greatest deformation, resulting in the spectacular vertical orientation seen today.
Sculpting the Fins: Erosion and Weathering Processes
Once the rock layers were tilted upright, they were exposed to erosion, which carved them into their present-day forms. The park’s distinct shapes result from differential erosion, where softer rock types wear away more quickly than harder, more resistant types. The uplifted layers consisted of alternating bands of durable, iron-oxide-cemented sandstones and softer shales and siltstones.
Over the last 5 million years, water, wind, and ice preferentially removed the less-resistant shales. This material washed away, forming the valleys and depressions that separate the towering structures. The more durable layers, such as the thick sandstones, were left standing as prominent, vertical ridges known as “fins” or “hogbacks.” Freeze-thaw cycles, where water expands as it freezes (ice wedging), slowly pried the rock apart. This physical weathering, combined with abrasive wind-blown sand, polished the fins into the spires and balanced rocks seen today.
Identifying the Rocks: Key Geological Formations
Several distinct rock formations contribute to the park’s vibrant palette and dramatic forms. The most voluminous layer is the Fountain Formation, a reddish-orange rock composed of arkosic sandstone and conglomerate derived from the ancient granite. Above this is the Lyons Sandstone, massive reddish-orange and white rocks formed from wind-deposited sand dunes. The Dakota Hogback, a prominent ridge, is composed of light-colored Dakota Sandstone that originated in shallow marine environments. The red and orange shades across the park are caused by iron oxide (rust), which acts as a natural cement binding the sand grains.