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25-657: The buttes are in the northeastern edge of the Colorado Piedmont . To the north, the piedmont is bordered by the Chalk Bluffs, an escarpment on the edge of the High Plains . As the rains and snows slowly erode the bluffs, the piedmont grows towards the north. Stream capture expands the piedmont rapidly towards the upslope or westward. The Buttes themselves are remnants of the High Plains surrounded by

50-909: A margin of land temporarily rose above the water along the ancestral Transcontinental Arch , each time rejoining the separated, divergent land populations, allowing a temporary mixing of newer species before again separating the populations. At its largest, the Western Interior Seaway stretched from the Rockies east to the Appalachian Mountains , some 1,000 km (620 mi) wide. At its deepest, it may have been only 800 or 900 metres (2,600 or 3,000 ft) deep, shallow in terms of seas. Two great continental watersheds drained into it from east and west, diluting its waters and bringing resources in eroded silt that formed shifting delta systems along its low-lying coasts. There

75-466: Is Monument Rocks , an exposed chalk formation towering 70 feet (21 m) over the surrounding range land. The Western Interior Seaway is believed to have behaved similarly to a giant estuary in terms of water mass transport. Riverine inputs exited the seaway as coastal jets, while correspondingly drawing in water from the Tethys in the south and Boreal waters from the north. During the late Cretaceous,

100-756: Is a harder mixture of sandstone and conglomerate , while the Brule layers are a softer clay. The surrounding area is considered a badlands as North Pawnee Creek cuts numerous channels into the Brule Formation soils. The Pawnee Buttes Trail is noted for its scenery and birdwatching potential. The Overlook, the Lipps Bluff trail, and the area within 200 yards of the cliffs are closed to hikers from March 1 to June 30, to protect nesting falcons , eagles , and hawks . Hikers are encouraged to keep away from these areas during that time to minimize disturbance to

125-664: Is an area along the base of the foothills of the Front Range in north central Colorado in the United States . The region consists of a broad hilly valley, just under 5000 ft (1500 m) in elevation, stretching north and northeast from Denver in the valley of the South Platte River , as well as along the Arkansas River valley southward from Colorado Springs . The name Colorado Piedmont also refers to

150-750: The Arctic Ocean transgressed south over western North America; this formed the Mowry Sea, so named for the Mowry Shale , an organic-rich rock formation . In the south, the Gulf of Mexico was originally an extension of the Tethys Ocean . In time, the southern embayment merged with the Mowry Sea in the late Cretaceous, forming a completed seaway, creating isolated environments for land animals and plants. Relative sea levels fell multiple times , as

175-730: The Larimer - Weld county line, the road drops noticeably from the Upper Cretaceous sandstone of the Plains to the lower shale of the Piedmont. The transition from High Plains to Piedmont is likewise accompanied by a change in agriculture, from pasture lands on the Plains to cultivated fields in the Piedmont. In the 19th century, the Piedmont region was inhabited primarily by the Southern Arapaho and Cheyenne tribes. From

200-909: The Cache la Poudre and other rivers, as well as the Colorado-Big Thompson Project , also supply needed water to the region. Cretaceous Sea The Western Interior Seaway (also called the Cretaceous Seaway , the Niobraran Sea , the North American Inland Sea , the Western Interior Sea and sometimes nicknamed "Hell's Aquarium" ) was a large inland sea that split the continent of North America into two landmasses for 34 million years. The ancient sea, which existed from

225-713: The Dakotas and retreated south towards the Gulf of Mexico . This shrunken and final regressive phase is sometimes called the Pierre Seaway . During the early Paleocene , parts of the Western Interior Seaway still occupied areas of the Mississippi Embayment , submerging the site of present-day Memphis . Later transgression, however, was associated with the Cenozoic Tejas sequence , rather than with

250-572: The Plains, rerouted northward along the mountains to join the Cache la Poudre River . In some areas of the Piedmont, a loose veneer of Pleistocene gravel overlays older shale and which accumulated during glaciation in the mountains, when streams descending onto the Piedmont became overburdened with sediment. The drop off from the Plains to the Piedmont is noticeable to motorists driving southward from Cheyenne, Wyoming on Interstate 25 . At approximately Mile 293 northeast of Wellington, Colorado , near

275-587: The Western Interior Seaway went through multiple periods of anoxia , when the bottom water was devoid of oxygen and the water column was stratified. At the end of the Cretaceous, continued Laramide uplift hoisted the sandbanks (sandstone) and muddy brackish lagoons (shale), thick sequences of silt and sandstone still seen today as the Laramie Formation , while low-lying basins between them gradually subsided. The Western Interior Seaway divided across

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300-946: The buttes is the Chadron member of the White River Formation. Above the Brule layer is the Pawnee Creek Formation from the Upper Miocene (20 mya). The cap of the buttes is the Arikaree Formation, also of the Miocene age. Research in the 1970s suggest that the upper level of the cap rock is of the Ogallala Formation from the Pliocene . The Pliocene layers exist further to the north in the High Plains region. The cap rock

325-471: The earliest time of white settlement in the middle 19th century, the issue of water has been a controlling force in the economy of the region. The use of irrigation in the Piedmont starting in the 1860s led to widespread homesteading and cultivation of wheat and sugar beets, as well as cattle and sheep ranching. Much of the irrigation water in the Piedmont comes from shallow wells that tap the layers of Pleistocene gravel. Water diversion projects, locally from

350-478: The early Late Cretaceous (100 Ma ) to the earliest Paleocene (66 Ma), connected the Gulf of Mexico to the Arctic Ocean . The two land masses it created were Laramidia to the west and Appalachia to the east. At its largest extent, it was 2,500 feet (760 m) deep, 600 miles (970 km) wide and over 2,000 miles (3,200 km) long. By the late Cretaceous, Eurasia and the Americas had separated along

375-608: The eastern side of the Rocky Mountains . The erosion scraped away the top layer of Upper Cretaceous sandstone (which still exists as the top layer on the High Plains), exposing the underlying layer of Pierre Shale , which had been formed during the Cretaceous, when a shallow sea covered present-day Colorado. It was during this time that the South Platte River, which had previously flowed eastward across

400-412: The flightless Hesperornis that had stout legs for swimming through water and tiny wings used for marine steering rather than flight; and the tern-like Ichthyornis , an early avian with a toothy beak. Ichthyornis shared the sky with large pterosaurs such as Nyctosaurus and Pteranodon . Pteranodon fossils are very common; it was probably a major participant in the surface ecosystem, though it

425-399: The massive 4-to-5-metre (13 to 16 ft) long Xiphactinus , larger than any modern bony fish . Other sea life included invertebrates such as mollusks , ammonites , squid-like belemnites , and plankton including coccolithophores that secreted the chalky platelets that give the Cretaceous its name, foraminiferans and radiolarians . The seaway was home to early birds, including

450-651: The nesting birds. The Pawnee Buttes feature proximately in James A. Michener's 1974 novel, Centennial . Dubbed the 'Rattlesnake Buttes' they form the backdrop for the nearby fictional town of which the novel is centred around. Subsequently the Pawnee Buttes are also utilised as a filming location for various scenes in the 1978 Centennial miniseries which is an adaption of James A. Michener's novel. [REDACTED] Media related to Pawnee Buttes at Wikimedia Commons Colorado Piedmont The Colorado Piedmont

475-669: The physiographic section of the Great Plains province . The Colorado Piedmont elevation is lower than the foothills, but is also slightly lower elevation than the High Plains to the east. According to current geologic theory, the Piedmont was formed approximately 28 million years ago, during the broad bowing of the North American Plate that lifted the continent between present-day Kansas and Utah to its present elevation of approximately 5000 ft (1500 m). This uplift resulted in increased streamflow and rapid erosion on

500-604: The piedmont. Another remnant of the high plains is to the west where the Chalk Bluffs form the eastern edge. The Buttes are a consolidation of several geological ages. The main mass of the butte is the lower half to two-thirds. It is a buff-colored layer from the Brule member of the White River Formation . It is from the Oligocene Epoch (25-40 mya). Below this level and visible only further east than

525-484: The previous event responsible for the seaway. The Western Interior Seaway was a shallow sea, filled with abundant marine life. Interior seaway denizens included predatory marine reptiles such as plesiosaurs , and mosasaurs . Other marine life included sharks such as Squalicorax , Cretoxyrhina , and the giant shellfish-eating Ptychodus mortoni (believed to be 10 metres (33 ft) long); and advanced bony fish including Pachyrhizodus , Enchodus , and

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550-403: The seaway. Many species can easily fit in the palm of the hand, while some like Inoceramus (Haploscapha) grandis could be well over a meter in diameter. Entire schools of fish sometimes sought shelter within the shell of the giant Platyceramus . The shells of the genus are known for being composed of prismatic calcitic crystals that grew perpendicular to the surface, and fossils often retain

575-454: The south Atlantic, and subduction on the west coast of the Americas had commenced, resulting in the Laramide orogeny , the early phase of growth of the modern Rocky Mountains . The Western Interior Seaway may be seen as a downwarping of the continental crust ahead of the growing Laramide/Rockies mountain chain. The earliest phase of the seaway began in the mid-Cretaceous when an arm of

600-481: Was found in only the southern reaches of the seaway. Inoceramids (oyster-like bivalve molluscs) were well-adapted to life in the oxygen-poor bottom mud of the seaway. These left abundant fossils in the Kiowa , Greenhorn , Niobrara , Mancos , and Pierre formations. There is great variety in the shells and the many distinct species have been dated and can be used to identify specific beds in those rock formations of

625-547: Was little sedimentation on the eastern shores of the seaway; the western boundary, however, consisted of a thick clastic wedge eroded eastward from the Sevier orogenic belt . The western shore was thus highly variable, depending on variations in sea level and sediment supply. Widespread carbonate deposition suggests that the seaway was warm and tropical, with abundant calcareous planktonic algae . Remnants of these deposits are found in northwest Kansas. A prominent example

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