The Pawnee Buttes are two prominent

butte __NOTOC__ In geomorphology, a butte () is an isolated hill with steep, often vertical sides and a small, relatively flat top; buttes are smaller landforms than mesas, plateaus, and tablelands. The word ''butte'' comes from a French word mea ...

s in northeastern

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

. The west butte is located within the

Pawnee National Grassland Pawnee National Grassland is a United States National Grassland located in northeastern Colorado on the Colorado Eastern Plains. The grassland is located in the South Platte River basin in remote northern and extreme northeastern Weld County be ...

, while the east butte is on private land in

Weld County Weld County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 328,981. The county seat is Greeley. Weld County comprises the Greeley, CO Metropolitan Statistical Area, which is included in the Denver ...

. Rising approximately above the surrounding plains, the buttes are erosional remnants left standing in isolation as the surrounding

High Plains High Plains refers to one of two distinct land regions: * High Plains (United States), land region of the western Great Plains *High Plains (Australia) The High Plains of south-eastern Australia are a sub-region, or more strictly a string of adja ...

surface has gradually worn away. The lower portions of the buttes are composed of relatively soft, clay-rich sedimentary rock called the Brule formation. The Brule formation is protected by an overlying layer of sandstone and conglomerate sediments called the Arikaree formation, which are more resistant to weathering.

Geology

The buttes are in the northeastern edge of the

Colorado Piedmont The Colorado Piedmont 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 northe ...

. To the north, the piedmont is bordered by the Chalk Bluffs, an escarpment on the edge of the

. 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 the piedmont. Another remnant of the high plains is to the west where the Chalk Bluffs form the eastern edge.An Interpretive Resource Analysis of Pawnee Buttes, Colorado; Dissertation; Robert Jack Badaracco; Colorado State University; Fort Collins, Colorado; March 1971 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 The White River Formation is a geologic formation of the Paleogene Period, in the northern Great Plains and central Rocky Mountains, within the United States. It has been found in northeastern Colorado, Dawes County in western Nebraska, Badlands ...

. It is from the Oligocene Epoch (25-40 mya). Below this level and visible only further east than the buttes is the Chadron member of the White River Formation. Above the Brule layer is the Pawnee Creek Formation from the Upper

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

(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 ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

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.

Vegetative zones

*‘’’Short Grass’’’ prairies surround the buttes. They are dominated by

Blue grama ''Bouteloua gracilis'', the blue grama, is a long-lived, warm-season ( C4) perennial grass, native to North America. It is most commonly found from Alberta, Canada, east to Manitoba and south across the Rocky Mountains, Great Plains, and U.S. ...

and

buffalo grass Buffalo grass may refer to * Buffalo grass, sweet vernal grass or vanilla grass ('' Anthoxanthum odoratum'') * Buffalo grass ('' Bouteloua dactyloides'') * Buffalo grass ('' Brachiaria mutica'') * Buffalo grass or sweet grass (''Hierochloe odorata' ...

. Associated plants include the Thread-leaf sedge, ring muhly,

western wheatgrass ''Pascopyrum'' is a monotypic genus of grass containing the sole species ''Pascopyrum smithii'', which is known by the common names western wheatgrass and red-joint wheatgrass, after the red coloration of the nodes. It is native to North America. ...

, and the prickly pear cactus. *‘’’Mixed Prairie’’’ are the lighter and more sandy soils, on the heights. The dominant plants are the Needle and thread grass,

, Junegrass, along with short grass plants. There is a wider mix of vegetation which becomes more noticeable in spring and early summer when Broom snakeweed, fringed sage, plus various

forbs A forb or phorb is an herbaceous flowering plant that is not a graminoid (grass, sedge, or rush). The term is used in biology and in vegetation ecology, especially in relation to grasslands and understory. Typically these are dicots without woo ...

, including milkvetches, and locoweeds are highly visible. The mixed prairie has the greatest variety of plants. *The ‘’’Little Bluestem’’’ is found across the entire grasslands, but it dominates in localized plots. These are in the swales and along north-facing slopes where the shade will retain water longer. Around the west butte, pockets are along the north and northeast facing slopes where the shade will retain water longer. These will also be

Little Bluestem ''Schizachyrium scoparium'', commonly known as little bluestem or beard grass, is a species of North American prairie grass native to most of the contiguous United States (except California, Nevada, and Oregon) as well as a small area north of t ...

and a mix of Canada rye,

Phlox ''Phlox'' (; Greek φλόξ "flame"; plural "phlox" or "phloxes", Greek φλόγες ''phlóges'') is a genus of 67 species of perennial and annual plants in the family Polemoniaceae. They are found mostly in North America (one in Siberia) in di ...

borges Jorge Francisco Isidoro Luis Borges Acevedo (; ; 24 August 1899 – 14 June 1986) was an Argentine short-story writer, essayist, poet and translator, as well as a key figure in Spanish-language and international literature. His best-known bo ...

, and a mix of grasses and forbs. *‘’’Clay Barrens’’’ surround the buttes, where the

Brule Formation The Brule Formation was deposited between 33 and 30 million years ago, roughly the Rupelian age (Oligocene). It occurs as a subunit of the White River Formation in Nebraska, Colorado, North Dakota, South Dakota, and Wyoming. It is a sequence of ...

is exposed. Here taproots dominate with hooker sandwort, tufted milk vetch, and common commandra. Several of these species use

rhizomes In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

to root spread following small fractures in the clays. Other plants associated with the Clay barrens are;

, Indian rice grass,

Penstemon ''Penstemon'' , the beardtongues, is a large genus of roughly 250 species of flowering plants native mostly to the Nearctic, but with a few species also found in the North American portion of the Neotropics. It is the largest genus of flowering ...

, and

evening primrose ''Oenothera'' is a genus of about 145 species of herbaceous flowering plants native to the Americas. It is the type genus of the family Onagraceae. Common names include evening primrose, suncups, and sundrops. They are not closely related to ...

. Where there is active erosion, there are no plants.
File:PawneeButtes_1900_USGS.jpg, Pawnee Buttes (1900)Darton, N.H. 1905. Preliminary report on the geology and underground water resources of the central Great Plains. United States Geological Survey, Professional Paper 32, 433 pp. (Plate 54-A) File:Pawnee Butte (West).JPG, West Pawnee Butte (2008) File:Pawnee Buttes.jpg, East and West Buttes Panoramic (2008)

Pawnee Buttes Trail

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

falcon Falcons () are birds of prey in the genus ''Falco'', which includes about 40 species. Falcons are widely distributed on all continents of the world except Antarctica, though closely related raptors did occur there in the Eocene. Adult falcons ...

eagle Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, just ...

s, and

hawk Hawks are bird of prey, birds of prey of the family Accipitridae. They are widely distributed and are found on all continents except Antarctica. * The subfamily Accipitrinae includes goshawks, sparrowhawks, sharp-shinned hawks and others. Th ...

s. Hikers are encouraged to keep away from these areas during that time to minimize disturbance to the nesting birds.

References

External links

{{commonscat-inline
USDA Forest Service Website for the Arapaho and Roosevelt National Forests, Pawnee National Grassland
Buttes of Colorado Protected areas of Weld County, Colorado Landforms of Weld County, Colorado

Geology

Vegetative zones

Pawnee Buttes Trail

See also

References

External links