Biscuit Hill

Biscuit Hill

If you look to the east from Natural Fort, you will see more sandstone outcroppings.  This is still part of the same material and geological process that formed Natural Fort.  What makes this little spot interesting is that just beyond the fence, probably a few hundred yards, is one of the largest and undisturbed sets of tipi rings in the area.  There we several inhabitants in this area at one time.  Several large tipi rings, hearths, rock, and earth mounds are still visible.  Should you decide that you would like to take a closer look, you will need to get permission and access from the Terry Bison Ranch, as it is on their property.

 

*Note: The Google maps will only take you so far on Terry Ranch Road before it wants to put you onto I-25.  If you follow the road past the ranch, it turns into a dirt road and just keep going until you get to Natural Fort and Biscuit Hill.

Natural Fort Colorado

Natural Fort

Wyoming sits on an escarpment known as the Gangplank.  This escarpment rises to the west toward the Rockies.  As you head south out of Wyoming into Colorado, you descend into the Colorado Piedmont.  This separates the mountains from the High Plains.  This area is mostly sandstone.  Just a few miles on I-25 south in Colorado you will notice sandstone outcrops on either side of the road, commonly referred to as Natural Fort.  This interesting piece of landscape is at the base of the Oligocene White River Formation.  These photos show how soft and easily erodible the sandstone is.  There used to a rest area at Natural Fort but it is no longer there.  The easiest way to get there is to take Terry Ranch Road out to the site.  

 

Glendo

Glendo Geology

            Like much of the plains of Wyoming, Glendo is made up of the Paleozoic and Mesozoic rocks that were carried by rivers to the area after being thrown from volcanic eruptions.  This area is different though because another event occurred here.  “Violent and prolonged volcanic eruptions in the Great Basin region of Nevada and eastern California” (Blackstone 113)  sent out volcanic ash that was carried by streams to finally settle as fine- grained sediment on the older Precambrian rock base.  Erosion from streams since then has revealed this history and has bared rocks from 30 million years ago.  There are also sand dunes that spread from this area into Nebraska.  The park has become a place of recreation with the Glendo Reservoir, the Sandy Beach, the North Platte River, and many campgrounds.

http://www.wallpaperdave.com/glendo.htm

Blackstone, D. L. Jr. Traveler’s Guide to the Geology of Wyoming.  The Geologic Survey of Wyoming: Laramie. 1988. 2^nd ed. 

Belvoir Ranch

Belvoir Ranch

While you are in the area, or on your way back to Cheyenne, you can cross Interstate 80 and to your south, you will see what is known as the Belvoir Ranch.  Go back to the Harriman (just follow the last map back), exit and turn south.  This is 18,800 acres of land purchased by the City of Cheyenne for development.  Geology of the Belvoir ranch is quite different in areas from across the street at Harriman or Vedauwoo.  While Vedauwoo is primarily Granite formation, to the south we find sandstone and limestone.  This is part of the Casper formation, which dates back 545 million years ago.  There appears to be a fault that rather follows a southwest to northeast direction.  You can clearly see the difference in rock on this side of the road.  Here you will find gray, tan and red sandstone, along with pink and gray limestone.  The first photo shows limestone on sandstone.  The second picture is of a prehistoric rock shelter found toward the south end of the property.  The third is  proof that the rock shelter was used by someone, possibly as far back as 11,000 years ago, to make stone tools.  It is a flake of chalcedony.  Supposedly there is a quarry of this material somewhere in the area, but we have not found it yet.  Given the size of the flake, it makes sense there are some large pieces in the area, as no one would tote stones that big around on the off chance he got some free time to make a tool.

 

 

Vedauwoo

Vedauwoo Geology

          The drive to Vedauwoo contains a gradual rise which is known as the Gangplank.  The rock formations seen from the highway draw attention right away.  Interestingly, those rocks are “precambrian granite and minor amounts of metamorphic rocks” (Blackstone 115).  The rocks in this area began with metamorphic rocks that were 1.7 billion years old.  These rocks were intruded on by the Precambrian granite, and the pink granite which is 1.4 billion years old has eroded the Sherman Granite.  It has all made for a beautiful site despite what it is made from.  There are distinct lines within many of the rock formations reflecting the dates of the layered rock as well as the erosion that has taken place in this area.

          Some of the formations have been given names like Turtle Rock where the rocks actually have a distinct shape.  The erosion here has also left many of the rocks in awkward states of balance.  The Sherman granite is what is mostly found here and this granite is coarse.  It contains biotite and hornblende.  There are at least three types of lichen in this area that I was able to take pictures of.  The weather was nice on the day we spent here and we were able to snap some nice pictures of the formations as seen below.  

Blackstone, D. L. Jr. Traveler’s Guide to the Geology of Wyoming.  The Geologic Survey of Wyoming: Laramie. 1988. 2^nd ed.

Harriman Quarry

Harriman Exit

            The first stop on this field trip is an exit off of I-80 that comes about 13 miles before Vedauwoo.  It is Exit 342 and it is approximately 18 miles from our home.  There is a quarry at this exit where the “Miocene Ogallala Formation, gently laps onto Precambrian granite” (Lageson 41).  This location is important because a lot of mining takes place here.  The quarries dig into the 1.4 billion-year-old Sherman granite.  This granite is able to be used to make ballast.  Ballast is a crushed aggregate that railroads use for “weighting and holding rail ties in place” (Lageson 41).  The pictures below were  taken from a distance because the quarry was blocked off so the camera zoom was relied upon.  Unfortunately, we were unable to get a closer look. 

Langeson, David R, Spearing, Darwin R. Roadside Geology of Wyoming. Mountain Press Publishing Company: Missoula. 1988.

History of Wyoming Geology

The History of Wyoming Geology

            The landscape of Wyoming has rocks dating back to over three billion years ago.  The geologic processes that took place in Wyoming are as varied as the landscape and many of them are not known because much of the erosion that has taken place has erased evidence of those processes.  Once covered by sea, the marine rocks have risen with crustal movement and the erosion since has weathered and carved the region into the Wyoming that is seen today.  The elevations in Wyoming vary from the highest point in “the summit of Gannett Peak (13,804 feet) in the Wind River Range and the lowest point (3,180 feet) in the channel of the Belle Fourche River in northeast Wyoming” (Blackstone 2).  Wyoming contains mountains, basins, and sits along the Continental Divide.  The Rocky Mountains make up a large part of the state, but this varies with the plains that roll east from the mountains. 

            There are many important geological features found throughout Wyoming.  One of the greatest is that of Yellowstone National Park.  This is a place of great interest, but the focus of this report will be on southeast Wyoming.  The plains can seem monotonous, but the rocky formations found throughout this region tell an important story of the history of this land and what has shaped it.  The gradual rise from the far southeastern side of the state toward the Laramie range is known as the Gangplank.  Much of the plains are formed from “flat-lying rocks of the Cenozoic and Mesozoic age” (Blackstone 8).  Most of these rocks were thrown from volcanoes and gradually carried east through river systems.  Those rivers and streams cut into those rocks and created many different geologic features.  The further east one goes, the more erosion they will see as the badlands are being created. 

            Overall, Wyoming offers a rich and diverse geologic history.  Through the study of locations within Wyoming, one can find themselves within a complex story of transition.  The features seen in Wyoming today speak about the ever constant change that has taken place not only in Wyoming, but all over Earth.  This speaks about the past while providing clues for possible changes in the future, and this is why it is so important to study even the tiniest of changes that occur.  

Blackstone, D. L. Jr. Traveler’s Guide to the Geology of Wyoming.  The Geologic Survey of Wyoming: Laramie. 1988. 2^nd ed.