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Laramide orogeny
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==Basins and mountains== The Laramide orogeny produced intermontane [[structural basin]]s and adjacent [[Horst (geology)|mountain blocks]] by means of deformation. This style of deformation is typical of [[continental plate]]s adjacent to [[convergent boundary|convergent margin]]s of long duration that have not sustained continent/continent collisions. This tectonic setting produces a pattern of compressive uplifts and basins, with most of the deformation confined to block edges. Twelve kilometers of structural relief between basins and adjacent uplifts is not uncommon. The basins contain several thousand meters of [[Paleozoic]] and [[Mesozoic]] [[sedimentary rock]]s that predate the Laramide orogeny. As much as {{convert|5000|m|sp=us}} of [[Cretaceous]] and [[Cenozoic]] sediments filled these orogenically-defined basins. Deformed [[Paleocene]] and [[Eocene]] deposits record continuing orogenic activity.<ref name=nasa>{{Include-NASA|title=Wyoming Intermontane Basins|url=http://daac.gsfc.nasa.gov/geomorphology/GEO_2/GEO_PLATE_T-8.shtml|archive-url=https://web.archive.org/web/20110617012733/http://daac.gsfc.nasa.gov/geomorphology/GEO_2/GEO_PLATE_T-8.shtml/|archive-date=2011-06-17|url-status=dead|first=M|last=Hegde}}</ref> During the Laramide orogeny, basin floors and mountain summits were much closer to sea level than today. After the seas retreated from the Rocky Mountain region, [[floodplain]]s, [[swamp]]s, and vast lakes developed in the basins. Drainage systems imposed at that time persist today. Since the [[Oligocene]], episodic [[epeirogenic movement|epeirogenic uplift]] gradually raised the entire region, including the Great Plains, to present elevations. Most of the modern topography is the result of [[Pliocene]] and [[Pleistocene]] events, including additional uplift, glaciation of the high country, and denudation and dissection of older Cenozoic surfaces in the basin by fluvial processes.<ref name=nasa /> [[File:Wpdms nasa topo bighorn basin.jpg|thumb|right|Topographic map of the western United States (and part of Canada) showing the Bighorn Basin (highlighted in orange), formed by the Laramide Orogeny]] In the United States, these distinctive intermontane basins occur principally in the central Rocky Mountains from [[Colorado]] and [[Utah]] ([[Uintah Basin|Uinta Basin]]) to [[Montana]] and are best developed in [[Wyoming]], with the [[Bighorn Basin|Bighorn]], [[Powder River Basin|Powder River]], and [[Wind River Basin|Wind River]] being the largest. Topographically, the basin floors resemble the surface of the western Great Plains, except for vistas of surrounding mountains.<ref name=nasa/> At most boundaries, Paleozoic through [[Paleogene]] units dip steeply into the basins off uplifted blocks cored by [[Precambrian]] rocks. The eroded steeply dipping units form [[hogback (geology)|hogback]]s and [[flatiron (geomorphology)|flatiron]]s. Many of the boundaries are [[thrust fault|thrust]] or [[reverse fault]]s. Although other boundaries appear to be [[homocline|monoclinal flexure]]s, faulting is suspected at depth. Most bounding faults show evidence of at least two episodes of Laramide ([[Late Cretaceous]] and [[Eocene]]) movement, suggesting both thrust and [[strike-slip]] types of displacement.<ref name=nasa/>
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