The Pembina Escarpment is a

scarp Scarp may refer to: Landforms and geology * Cliff, a significant vertical, or near vertical, rock exposure * Escarpment, a steep slope or long rock that occurs from erosion or faulting and separates two relatively level areas of differing elevatio ...

that runs from South Dakota to Manitoba, and forms the western wall of the

Red River Valley The Red River Valley is a region in central North America that is drained by the Red River of the North; it is part of both Canada and the United States. Forming the border between Minnesota and North Dakota when these territories were admitted ...

. The height of the escarpment above the river valley is .

Geology

The escarpment was originally formed by the undercutting of Cretaceous sandstones (the

Dakota Formation The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Wester ...

) by the ancestral Red River. The escarpment was later steepened by glacial scouring. The escarpment is preserved due to a layer of erosion-resistant shale (the Pierre Formation) on top of the sandstone. The vista today, of wooded hills with small farms tucked into valleys (such as the

Pembina Valley The Pembina Valley (french: Vallée-de-la-Pembina) is an informal geographic region of the Canadian province of Manitoba. It is named for its major geographical feature, the Pembina Valley, which runs through the southwestern part of the region. ...

), is reminiscent of pastoral sections of New England. Streams flowing off the escarpment have high gradients and a cobble substrate. The final form of the escarpment we know today was not created until the end of the last ice age around 12,000 years ago. During the ice age, much of North America was covered by the Laurentide Ice Sheet. As the

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at L ...

began to melt and recede, the meltwaters filled the ancestral Red River Valley to create

Lake Agassiz Lake Agassiz was a large glacial lake in central North America. Fed by glacial meltwater at the end of the last glacial period, its area was larger than all of the modern Great Lakes combined. First postulated in 1823 by William H. Keating, i ...

. The valley walls, including the escarpment to the west, provided east and west boundaries for the lake, and remaining part of the ice sheet provided the northern boundary. During this period of time—known as the Lockhart Phase of Lake Agassiz—water flowed south from the lake into the Mississippi River and into the Gulf of Mexico.

Geography

In the US, the Pembina Escarpment is a Level 4 ecoregion, as defined by the U.S. Environmental Protection Agency. The ecoregion covers , and is part of the Level 3 Northern Glaciated Plains ecoregion. In Canada, the Pembina Escarpment is considered an Ecodistrict within the Southwest Manitoba Uplands Ecoregion, and the Southwest Manitoba Uplands Ecoregion is part of the Prairies Ecozone. A Canadian Ecodistrict is equivalent to a US Level 4 Ecoregion and a Canadian Ecoregion is equivalent to a US Level 3 Ecoregion. A Canadian Ecozone is equivalent to a US Level 1 Ecoregion. Both the US and Canada consider Turtle Mountain to be a sibling ecodistrict with the Pembina Escarpment, as both countries place both areas within the same larger ecoregions. Some US sources use the term "Manitoba Escarpment" for the Canadian portion of the Pembina Escarpment, but in Canada, the term

Manitoba Escarpment The Manitoba Escarpment, or the Western Manitoba Uplands, are a range of hills along the Saskatchewan-Manitoba border. The eastern slopes of the range are considered to be a scarp. They were created by glacial scouring and formed the western s ...

refers to a separate geographical region along the Saskatchewan-Manitoba border. The Pembina Escarpment is separated from the

by the

Assiniboine The Assiniboine or Assiniboin people ( when singular, Assiniboines / Assiniboins when plural; Ojibwe: ''Asiniibwaan'', "stone Sioux"; also in plural Assiniboine or Assiniboin), also known as the Hohe and known by the endonym Nakota (or Nakoda ...

and Souris River valleys, which were covered by

Lake Souris A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larg ...

at the time of Lake Agassiz when both escarpments were formed.

Ecology

Before the Europeans

settled A settler is a person who has migrated to an area and established a permanent residence there, often to colonize the area. A settler who migrates to an area previously uninhabited or sparsely inhabited may be described as a pioneer. Settle ...

in this region, the slopes and peaks of the escarpment were largely covered by a deciduous forest of

burr oak ''Quercus macrocarpa'', the bur oak or burr oak, is a species of oak tree native to eastern North America. It is in the white oak section, ''Quercus'' sect. ''Quercus'', and is also called mossycup oak, mossycup white oak, blue oak, or scrub oa ...

and trembling aspen. The wetter, cooler, shadier slopes had more aspen, and the drier, warmer, sunnier slopes had more oak. The shrubbery along the slopes consisted of

beaked hazel ''Corylus cornuta'', the beaked hazelnut (or just ''beaked hazel''), is a deciduous shrubby hazel with two subspecies found throughout most of North America. Description The beaked hazelnut can reach tall with stems thick with smooth gray b ...

, high bush cranberry,

saskatoon berry ''Amelanchier alnifolia'', the Saskatoon berry, Pacific serviceberry, western serviceberry, western shadbush, or western juneberry, is a shrub with an edible berry-like fruit, native to North America. Description It is a deciduous shrub or sma ...

, and pin cherry. The areas along rivers and creeks with more moisture had

Manitoba maple ''Acer negundo'', the box elder, boxelder maple, Manitoba maple or ash-leaved maple, is a species of maple native to North America. It is a fast-growing, short-lived tree with opposite, compound leaves. It is sometimes considered a weedy or inv ...

green ash ''Fraxinus pennsylvanica'', the green ash or red ash, is a species of ash native to eastern and central North America, from Nova Scotia west to southeastern Alberta and eastern Colorado, south to northern Florida, and southwest to Oklahoma and e ...

red osier dogwood ''Cornus sericea'', the red osier or red-osier dogwood, is a species of flowering plant in the family Cornaceae, native to much of North America. It has sometimes been considered a synonym of the Asian species '' Cornus alba''. Other names incl ...

and willows. Native vegetation has largely been cleared to make way for agriculture, but still exists on steep slopes and near water where farming is difficult.

References

External links

* {{Authority control Landforms of Manitoba Landforms of North Dakota Landforms of South Dakota Escarpments of the United States Escarpments of Canada