Ft. Hays Limestone

This EarthCache is located in Red Rock Canyon Open Space, one of the newer parklands of the City of Colorado Springs. You will be hiking the Hogback Valley Trail on the east side of the park, with access from U.S. 24, or 31st Street. The aim of this EarthCache is to get a good look at the Ft. Hays Limestone, and familiarize yourself with some of its characteristics. This is a 2-part EarthCache, with a hike of 0.6 mile between points, and a gain in elevation of about 150’. Remember to bring water for your hike, and a ruler or other measuring device. Please remember that fossils in the Red Rock Canyon Open Space are protected and that collecting is not allowed!

38 50.866 104 52.438 Contact with the Ft. Hays Limestone and Codell Sandstone

This EarthCache begins at a good view point of the contact zone of the Ft. Hays Limestone with the Codell Sandstone. The Ft. Hays Limestone is the basal member of the Niobrara Formation, an upper Cretaceous marine formation deposited in the Western Interior Sea about 87 million years ago. It is made up of beds of relatively resistant chalky limestone separated by alternating beds of softer chalky shale (it is for this reason that the Niobrara Formation is sometimes referred to as the Niobrara Chalk). The limestone is the white formation which is to your left as you look westward toward the hogback.

Ft. Hayes Limestone was formed from the calcareous remains of millions of clam shells that came to rest on the bottom of the Interior Sea. Like most sedimentary rocks, the deposition of these layers occurred in a horizontal manner. After successive layers of sediments covered this material, heat and pressure caused it to lithify into limestone. About 20 million years after this deposition, the Laramide Orogeny began, lifting up the Rocky Mountains, and causing the nearby sedimentary layers to be tilted into an almost vertical position. After the top layers eroded away, the ridges were exposed which are now visible before you.

Interestingly, the Ft. Hays Limestone has been utilized to determine climate and climatic change during the upper Cretaceous period. This is possible because the alternating limestone and shale beds are thought to have been caused by rhythmic sedimentation (also called cyclotherms) in the Western Interior Sea. The cyclotherms were associated with wet and dry periods which were caused by differences in the precession and orbital eccentricity of the Earth.

Codell Sandstone is the tan formation to the right of the limestone. It is a member of the Benton Shale, and ages to approximately 90-92 million years old. It, too, is a product of the Western Interior Sea, and was formed from coastal deposits made up of sandbars, barrier islands, and marine shelf sands. Ammonites and sharks teeth are common fossils found in this formation.

Question 1. From these coordinates, walk over to the point at which the Ft. Hays Limestone and Codell Sandstone come into contact. Feeling both the limestone and sandstone, which do you think is the harder material?

Question 2. Note the difference in the limestone and shale layers of the Ft. Hays Limestone. Beginning at the contact with the Codell Sandstone, count the number of limestone layers which are visible.

From this location, walk southerly along the Hogback Valley Trail. This trail will lead you through the shale and limestone beds as you gain in elevation. Always to your right will be near-vertical beds of limestone forming a wall on the east side of the hogback.

38 50.367 104 52.641 Shells, Shells, and more Shells

At this site, you will be very close to one of the basal layers of limestone and you can easily see several clam shells that make up this layer. Walk over to the limestone layer and answer the following:

Question 3. How many shells can you see here, and what is the diameter of the largest one?

Question 4. What do clam shells tell you about the marine conditions at the time these beds were laid down?

To log this EarthCache: Send me an email answering the questions from the 2 stops. These are listed as follows:

1. Feeling both the limestone and sandstone, which do you think is the harder material?
2. How many layers of limestone do you see here?
3. How many shells can you see here, and what is the diameter of the largest one?
4. What do clam shells tell you about the marine conditions at the time these beds were laid down?

Please consider posting photos of yourself, or the local geology, when you log this EarthCache. Photos can be an additional rewarding part of your journey, but posting them is not a requirement for logging this EarthCache, and is strictly optional.

The above information was compiled from the following sources:

2009. Everhart, M. First Polycotylid Remains from the Fort Hays Limestone. Online at Oceans of Kansas: http://www.oceansofkansas.com/FHSM_VP-16459.html

2005. Everhart, M. Earliest record of the genus Tylosaurus (Squamata; Mosasauridae) from the Fort Hayes Limestone (Lower Coniacian) of western Kansas. Transactions of the Kansas Academy of Science 108(3): 149-155. Online at: http://www.bioone.org/doi/full/10.1660/0022-8443(2005)108%5B0149%3AEROTGT%5D2.0.CO%3B2

Climate Archives. Online at the Boise State University Department of Geosciences Website: http://earth.boisestate.edu/

2004. Hopkins, R.L., and L.B. Hopkins. Hiking Colorado’s Geology

Colorado Springs City Webpage: Red Rock Canyon Open Space: http://www.springsgov.com/page.asp?NavID=4069

Geologic Map of the Red Rock Canyon Area: http://www.redrockcanyonopenspace.org/page10a.html

Thanks to the City of Colorado Springs and the Parks, Recreation & Cultural Services Department for allowing placement of this EarthCache!