THE HIGH PLAINS: FULL OF CHARACTER

At times during my daydreaming sessions certain mental cues dredge up many memories from my childhood!   One common memory is the excitement associated with the road trip from the hot plains of Kansas to the cool temps of the Colorado mountains.  I suppose this trip was more of a joy to my mother than the kids for we lived frugally and air conditioning was not installed in our tiny home. So, my father got us up early one morning in late summer and we headed west with sandwiches and “pop” in a cooler and three “kids” in the backseat arguing about “who got to sit by a window.”  As the eldest, there was not a question about my authority and the right back window was always mine.  In pre-Interstate 70 days my brothers and I always pleaded with them to stop at the Tower near the city of Limon so we could see the mountains (early on we always thought the mountains magically appeared at the state line).  Well, out of necessity my father was a frugal man so we always passed up this opportunity at the Tower.  He was more interested in free attractions such as “rattlesnakes in a box” with the appropriate sign on top—“Don’t Tap on the Cage.”  Of course that little bit of information always encouraged him to tap!  Other bits of frugality included making a U-turn at Seven Falls (they charged admission) and heading over to Helen Hunt Falls (free).  I suppose I inherited some of those traits since my son once told me (as an adult) that he stopped at the Tower (and also the “largest prairie dog in the world” at Oakley, Kansas) since I never wanted to stop and spend the money and therefore, he had suffered and missed out on seeing major attractions as a child!

OK, why can you see for long distances from the Tower, or actually just as well from the road!  At that particular locality, at the hamlet of Genoa east of Limon,  you are crossing over the High Plains Escarpment down to the dissected and eroded Colorado Piedmont.  Both of these physiographic regions  are part of the much more extensive Great Plains Physiographic Province (GPPP), and that needs an explanation. 

Satellite image of an area near Limon, CO.  The High Plains are well defined to the east by the presence of “squares” of farmed land.  The Colorado Piedmont to the west is generally used for grazing.  The High Plains Escarpment is the boundary between the two provinces.  The “arrowhead” of High Plains projecting west is known as Cedar Point.  Photo courtesy of Yahoo Maps©.

The GPPP extends from southern Canada (Manitoba, Alberta, Sakatchwean) south to the Rio Grande River, an area about 500 miles wide by 2000 miles in length.  The Great Plains are the major grasslands and prairies of North America but also include many other regions: the Black Hills of South Dakota and Wyoming, a Laramide (late Cretaceous and early Tertiary) dome/anticline with a core of Precambrian granite surrounded by successively younger Paleozoic and Mesozoic rocks; the Missouri Plateau (Coteau du Missouri)--glaciated--, a geomorphically complex region in eastern South Dakota, eastern and northern North Dakota, and northeastern Montana.  It is an area that experienced several episodes of continental glaciation in the Pleistocene (Ice Age) and the topography is rolling and dotted by glacial lakes (kettles); the Missouri Plateau—unglaciated—in western South and North Dakota, northeastern Wyoming and southeastern Montana.  The Missouri River flowing through these states is essentially an ice marginal river and seperates the unglaciated landscape from the glaciated region.  In contrast to the rolling glaciated region, the unglaciated province has  a variety of spectacular landforms and is one of my favorite areas.  There are volcanic buttes such as Bear Butte (South Dakota) and Devils Tower (Wyoming), laccolithic mountains (intrusive igneous bodies with a mushroom shape) such as the Big Belt and Little Belt Mountains (Mountana), mountains floored by large igneous intrusions termed stocks such as the Big Snowy Mountains, Crazy Mountains, and Castle Mountains (Montana), mountains formed by both volcanic flows and intrusions such as the Bearpaw Mountains (Mountana), eroded Tertiary sedimentary rocks forming “badlands” (North Dakota and South Dakota), and a plethra of large river valleys and isolated buttes; the Plains Border Section is a badly dissected (streams) area in central Kansas and north-central Oklahoma that forms the eastern boundary of the GPPP;  the volcanic-rich Raton Section; the Pecos Valley in eastern New Mexico and southwestern Texas generally floored by Paleozoic rocks and displaying a karst topography (caves and sinkholes) with the most famous being Carlsbad Caverns; the dissected Colorado Piedmont; the High Plains; the, area in Central Texas around the Llano Dome where Precambrian rocks are exposed; and the Edwards Plateau, an area primarily with outcrops of Cretaceous limestone and lying south of the Central Texas Uplift and east of the Pecos Valley.

Sketch map of the Great Plains Physiographic Province (U. S. portion) showing subdivisions.  Map from Trimble, 1980.

In past years American Bison occurred by the millions on the prairies.  Today, much of the production of hydrocarbons (oil and coal) in the U. S. comes from the Great Plains.  Geologically speaking,  a large portion of the GPPP coincides with the location of the Western Interior Seaway (WIS) and outcrops of Cretaceous age rocks are widespread, fossiliferous, and often spectacular.

In Colorado, the GPPP is divided into the High Plains Section, Raton Basin/Section, and the Colorado Piedmont.  The GPPP extends from the edge of the mountains, the front ranges, eastward to the state line (and beyond). 

Paleogeographic map of the late Cretaceous showing locations of the Western Interior Seaway and the future GPPP.  Map from Trimble, 1980.

The High Plains is essentially defined, in a geological manner, by outcrops of the Miocene-Pliocene Ogallala Formation, clastic sediments (now sandstones, conglomerates, shales) deposited by a series of streams flowing eastward from the rising Rocky Mountains.  This uplift was not the Laramide Orogeny that is of late Cretaceous and early Tertiary age, but a more regional uplift whereby the entire region was broadly lifted up.  Geologists also see evidence of this uplift in other ways besides the debris shed to the east (the Ogallala Fm.) such as the accelerated canyon cutting in areas like the Royal Gorge and Black Canyon of the Gunnison.  Originally, the Ogallala sediments extended from the mountains to perhaps the far eastern part of Kansas, a vast gently sloping plain, and from South Dakota to Texas.  Today, only small isolated remnants are left east of central Kansas as numerous modern river systems have completely destroyed and eroded away the eastern sections.  The High Plains is actually somewhat of a “flat” plateau commonly bounded by escarpments (cliffs).  On the eastern edge in Kansas the Fort Hays Escarpment (composed of the Cretaceous Fort Hays Limestone Member of the Niobrara Formation) generally marks the limits of Ogallala outcrops.  This boundary, in a general way, coincides with the 100^th Meridian, the 20 inch rainfall line, and the 2000 foot contour line—the beginning of The American West.  The southern boundary is an escarpment breaking down from the southern High Plains (the Llano Estacado region) to the Edwards Plateau (an area of Cretaceous rocks) in Texas.  The northern boundary in Nebraska and southern South Dakota is known as the Pine Ridge Escarpment and is a very prominent topographic feature. Along the Rocky Mountain system the Ogallala Formation has been eroded away except for one small remnant near Cheyenne, Wyoming.  In Colorado, the High Plains extends from near Limon eastward to the state border, and beyond, and occupy the eastern part of the state.  It is a rather flat area with little relief and a flora of short grasses and little rain fall.  Wind blown clay (loess) and sand mantle much of the bedrock.  The South Platte and Wray dune fields cover about 5000 sq. mi. in the northeastern part of the state.  Travelers on I-70 notice little relief in the topography since major streams drain east and the roadway is constructed on the interflueves, areas between the streams.  

The Fort Hays Escarpment, western Kansas, where the traveler “drops off” the High Plains east to the Plains Border Section.

In contrast to the short grasses found at the eastern boundary of the High Plains in Kansas, the northern boundary, Pine Ridge Escarpment, is forested.  Photo Public Domain.

The southern boundary of the High Plains is located at the Caprock Escarpment in Texas where the flat Llano Estacado (Staked Plains) transitions to the dissected Edwards Plateau.  Photo Public Domain.

However, the High Plains is interesting for many reasons, not the least of which is the fact that the surface underneath the sand and loess has remained relatively unchanged for the last five million years or so (Trimble, 1980).

That brings us to the western boundary of the High Plains, the Colorado Piedmont, and the Tower.  As noted above, the Ogallala, at one time, extended westward to the mountain front.  However,  in the Colorado Piedmont the Ogallala has been eroded away and the landscape is one of rolling hills and valleys with exposures of Cretaceous rocks.  The general elevation of the eastern part of the Piedmont is around 5000 feet and this explains the view from the Tower.  The location of the Tower at Genoa marks the end of the High Plains, with an elevation at Genoa of 5604 feet.  There is a noticeable dropoff  from the High Plains down to the Piedmont and this is quite evident when driving I-70 and reaching what is called the High plains Escarpment.  So, the view to the west is no different than standing on a high hill.  Can you actually see six states that I presume to be Colorado, Kansas, Nebraska, Wyoming, New Mexico, and South Dakota!  WOW.  Your call!  

High Plains Escarpment near Genoa, CO.  The High Plains (right, east), with outcrops of the Ogallala Fm., and the lowlands of the dissected Colorado Piedmont (in distance). 

One very interesting area in far northeastern Colorado is termed the Pawnee Buttes.  These high buttes are erosional remnants of the High Plains left isolated by eastern retreat of the Plains.  Pawnee Buttes have a caprock of Ogallala Formation covering the Miocene Arikaree Formation and the Oligocene White River Group.  The Buttes have produced well-known fossil vertebrate faunas.

North of Colorado Springs is a small subprovince of the Piedmont termed the Monument/Palmer Divide, an eastward extending ridge held up by late Cretaceous sandstones with elevations ranging from 6000 feet on the eastern edge to 7500 feet on Monument Hill.  This range of hills is the drainage divide between the South Platte River to the north and the Arkansas River to the south.  Tributaries of these rivers have been, and are, eating/eroding in both north and south directions but have not connected.  Perhaps either river will capture streams of the other in the future.  One could dream that the Arkansas River, at an elevation of ~4660 feet at Pueblo, might capture the South Platte River flowing at an elevation of ~5200 feet in Denver!  However, in today’s complex world I doubt if the Corps of Engineers would let that little bit of thievery take place.

Pawnee Buttes in northeastern Colorado are erosional remnants of the High Plains preserved on the Colorado Piedmont.  Photo taken in 1900 by U. S. Geological Survey.

Roadside America.com has perhaps the best description of the Tower: “From a mile away the Wonder Tower appears to be bustling. ‘See Six States!’ yell the hand-painted signs. ‘Confirmed by Ripley!’ One sees cars in the parking lot, and people at the top of the Tower, trying to see the advertised six states.
Once you arrive, you realize …the people in the Tower are crude fakes - lumps of red sheets wearing sunglasses.
The Wonder Tower, built in 1926 at the highest point between New York and Denver, was once a major stop.” 
  

The Tower near Genoa, Colorado.

Unfortunately, the construction of those vast ribbons of concrete, the Interstate highways, has obliterated most “mom and pop” tourist attractions and I believe the nation is poorer for the loss.  The last time I journeyed by the Tower it appeared closed, not unlike the rattlesnake cages along Route 66 in Arizona.

Another item lacking along the Interstate highways are those single picnic tables situated under a giant cottonwood tree with a well-used trash barrel (an “oil” barrel with the top chiseled off).  It was at these pleasant rests that we stopped to enjoy our baloney sandwiches on cheap white bread with mustard, a bag of greasy potato chips, a jar of homemade dill pickles, cupcakes for dessert, and the “pop.”  What more could a kid from the flatlands ask for?  
  

Roadside Park near St. Louis Park, Minnesota.  This park is considerable larger than the single picnic tables and a lone cottonwood tree found in western Kansas and eastern Colorado.  Of course, the population base is larger and trees more numerous than on the Plains.  Photo Public Domain but courtesy of St. Louis Park Historical Society.

These eastern grasslands [of Colorado] lack Aspen’s panache and dazzle; they don’t dress the part of High Society in Denver, and have been misunderstood and mistreated accordingly…  They are not loaded with flamboyant landforms, breathtaking rock sculptures, dancing waterfalls.  Instead they have a sparse, sinewy beauty, full of character, that does not depend on a pretty face…oblivion may be the only way they will retain their intrinsic character and not be tarted up by come-on neon signs and gambling palaces…

 Ann Zwinger, Colorado

REFERENCES CITED

Trimble, D. E., 1980, The Geologic Story of the Great Plains: U. S. Geological Survey Bulletin 1493.