Glossary for Garden of the Gods Geology
The Garden of the Gods is composed of clastic and chemically precipitated sedimentary rocks.
Clastic - Fountain Arkose, Lyons Sandstone (both red and white) Lykins (shales), Morrison shales and clays, Dakota Group, Benton Group, and the Pierre Shale
Chemical Precipitates - Lykins (limestone and dolostone), gypsum member of lower Morrison Formation, and the limestone in the Niobrara Formation.
It is a geologic principal that most layers of sedimentary rock were initially deposited horizontally. We know that because sediment now being deposited in stream valleys, lakes and the sea is spread out (generally) in horizontal layers. Geologists rely on this principal to analyze sedimentary layers that are no longer horizontal, like those in the Garden of the Gods, and conclude that they have been deformed.
Using this information, we assume that each new sedimentary layer is deposited over the one beneath it. This is the basic geological principal of superposition, which says that the order in which sediment is deposited is from bottom to top.
Beginning in the western portion of the Garden, the oldest strata (layers) are found. As one travels eastward in the park, the rocks become younger.
Beginning with the oldest rocks, descriptions are:
Fountain Arkose- The word "arkose" means the rock contains at least 25% feldspar. The Fountain Arkose is a conglomerate of very coarse-grained sediments. Individual quartz grains may be four or more inches in diameter. This formation represents the only direct evidence of the Ancestral Rocky Mountains, deposited from stream gravels as those first mountains eroded. Balanced Rock, Siamese Twins, Cathedral Spires and Three Graces are examples of rock formations found in this rock layer.
Lyons Sandstone - The change from the Fountain Formations to the Lyons is gradational. The Lyons is fine-grained quartz sandstone, much of which is cross-bedded (evidence of deposits in various different directions). Cross bedding is found among meandering stream deposits, sand dunes, and along beaches. The angle of the deposits in some layers and size of the sand grains suggest that the Lyons is solidified sand dunes. Kissing Camels, South Gateway Rock, Cathedral, and the Sleeping Giant are Lyons Sandstone. The colors are different in these rocks due to the amount of iron oxide present.
Lykins Formation - The Lykins Formation consists of red, thin-bedded, sand siltstones and shales, including gray, "crinkly" dolostone and limestone layers. These crinkly layers are fossil algae known as Stromatolites. The limestone, dolostones, siltstones, and shales formed in a marine environment.
Morrison Formation - The Morrison Formation consists of clays, siltstones, and carbonates (e.g. gypsum) which accumulated in a warm, moist lowland environment. Sluggish rivers were responsible for the deposit of mud and silt, which hardened into shale and siltstone respectively. Gypsum forms from the evaporation of a warm shallow sea. The dense, granular form of gypsum is called alabaster, and has been carved into ornaments and pottery. Chalk and plaster of paris are also made of gypsum.
The Morrison Formation is significant because it yielded some of the world's first dinosaur fossils, in 1877, from Morrison, Colorado. The skull of a Camptosaurus was found in this formation within Garden of the Gods in 1886. A replica of this Jurassic herbivore's fossilized skull is on display at the Visitor Center. This formation can be seen as the purple, maroon and gray clays and shales in the roadcuts just before the North Main Parking Lot.
The small white hills on the Ridge Trail represent the lower part of the Morrision Formation and consist of gypsum.
Purgatoire Formation - Part of the Dakota Group, this formation consists of a "bleached" sandstone member and a shale and siltstone member. The only place the Purgatoire Formation outcrops in the Garden of the Gods is the small hill immediately behind the Ute Indian Trail marker. It is thought that the sands of this formation were deposited in a flood plain environment.
Dakota Sandstone - Also part of the Dakota Group, this sandstone is a marine sandstone. It was probably deposited on or near a beach environment. The Dakota consists of buff, yellow, and gray cross-bedded sandstone, interbedded with gray shales. Much of the petroleum for Colorado and Wyoming, and water for these states and Nebraska is pumped from the Dakota Formation.
Benton Group - The Benton Group is a result of a shallow sea that ran over the beach sands (see Dakota Formation above). This group consists of formations of shale, limestone, and shale in sequence from bottom to top (west to east in the Garden). The soft shales of the Benton Group are easily eroded. This erosion formed the valley west of Rock Ledge Ranch.
Niobrara Formation - As the sea deepened, the deposited sediments became finer. The shales gave way to deep-water sediments - limestone. The limestone of the Niobrara Formation is abundant in marine fossils; sharks teeth are common. The ridge immediately west of Rock Ledge Ranch is part of the Niobrara Formation.
Pierre Shale - Above the Niobrara Formation lie the fine gray muds of the Pierre Shale. The Pierre Shale, totaling about 5,000 feet, is the thickest formation in the Colorado Springs area; most of the metropolitan area of Colorado Springs is built on the exposed surface of the Pierre Shale. Fossils in this formation include clams, ammonites, and bones of fossil fish.
This ends the rock sequence in the Garden of the Gods. Many other rock formations in the region come before and after these particular layers.
Laramide Orogeny, or How the Rocks Were Tilted Upward...
If all these sediments and more were deposited horizontally, how were the sedimentary rocks in the Garden tilted vertical?
The word orogeny means mountain building; hence, Laramide Orogeny simply means mountain building during the Laramide time. (to see the timeline again, click here)
As the land begins to rise, and the Front Range is uplifted, the layers of rocks on top are bent upward.
Subsequent erosion removed most of the strata (layers) as the mountains rose.
It is important to remember that the rocks of the Garden were tilted while deep underground. Erosion removed the surrounding softer rocks e.g. shales) exposing the rocks we see today.
According to most authorities, the Laramide Orogeny occurred about 70 million years ago. While there are periods of stillness, uplift is probably still occurring.
Faulting, or Why the Rocks Aren't All Tilted at the Same Angle
A fault is a break in the rock along which relative movement has occurred. The Garden of the Gods is extremely faulted. This faulting is a result of stress in the strata (layers) during the Laramide Orogeny. The consequence of this stress is that the rocks in the Garden are often vertically, laterally and diagonally moved and may seem out of sequence.
The reason the rocks in the immediate Garden area are vertical and the rocks to the west slant at only 20-45 degree angles can be attributed to the Rampart Fault. This fault follows the base of the eastern face of the Rampart Range in a north-south trend. The southern most end of the fault lies near Bear Creek Park. The Rampart Fault appears to be a fault "zone" several hundred feet wide with extreme vertical tilting of the rock along the zone. Therefore, the initial tilting of the rocks was because of orogeny. But, additional faulting caused the rocks in the Garden to be vertical and overturned.
Erosion and Landforms
Erosion is defined as the transportation of weathered rock material by wind, running water, ice or gravity. When rock material moves to another place, it creates a landform where it is deposited (erosional landforms). The Lyons Sandstone in the Garden was originally deposited into dunes (depositional landform), buried beneath more sediment, solidified and later exposed through the processes of erosion to their current forms (erosional landforms).
The Garden of the Gods exists today as remnants of differentially eroded bedrock. Differential erosion is defined as selective removal of rock material in accordance to erosive susceptibility and agency. This means that the hardness of rock material is partly related to its ability to withstand erosive forces of wind, water and ice in a particular climate. For example, shale and mudstones erode more easily than sandstone.
Landforms and Denudation
Landforms such as mountains, hills, valleys and plains are distinct relief features of the land surface.
Denudation is where weathering and erosion wears away and lowers the rocks and land. Water is by far the most dominant factor. Even in most arid regions, water is primarily responsible for shaping the land.
Generally speaking, in the western United States, strata (layers) of sandstone and limestone will form ridges and hogbacks. Shales, mudstones and siltstones will erode to form valleys.
If, instead of the arid climate found in the Garden of the Gods, the climate was a moist one of high rain and snow, the towering formations would have deteriorated much more rapidly through time. Today's Garden of the Gods would probably be sandy soil with towering trees instead of towering rocks!