Texas

===Geology===
{{main|Geology of Texas}}
[[File:Palo Duro lighthouse.jpg|alt=|thumb|[[Palo Duro Canyon]]]]
[[File:Summitanthonysnose1b.jpg|thumb|[[Franklin Mountains State Park]]]]
[[File:Big Bend National Park PB112599.jpg|thumb|[[Big Bend National Park]]]]
Texas is the southernmost part of the Great Plains, which ends in the south against the folded [[Sierra Madre Occidental]] of Mexico. The [[continental crust]] forms a stable [[Mesoproterozoic]] [[craton]] which changes across a broad continental margin and transitional crust into true [[oceanic crust]] of the Gulf of Mexico. The oldest rocks in Texas date from the Mesoproterozoic and are about 1,600&nbsp;million years old.<ref>{{cite web|title=Geology|url=https://www.nhnct.org/geology/geo1.html|access-date=December 28, 2020|website=nhnct.org}}</ref>

This margin existed until [[Laurasia]] and [[Gondwana]] collided in the [[Pennsylvanian (geology)|Pennsylvanian]] subperiod to form [[Pangea]].<ref>{{cite web|date=2016|title=Late Cretaceous and Tertiary Burial History, Central Texas|url=https://static1.squarespace.com/static/56e481e827d4bdfdac7fbe0f/t/58c1e3fac534a59cc49605f6/1489101856226/Rose%2C+P.%2C+2016%2C+Late+Cretaceous+and+Tertiary+Burial+History%2C+Central+Texas%2C+GCAGS.pdf|access-date=December 28, 2020|website=gcags.org|quote=Fault displacement decreases steadily to the north of Austin and to the west of San Antonio; Balcones faulting dies out about halfway between Waco and Dallas, and about halfway between Uvalde and Del Rio.}}</ref> Pangea began to break up in the [[Triassic]], but [[seafloor spreading]] to form the Gulf of Mexico occurred only in the mid- and [[late Jurassic]]. The shoreline shifted again to the eastern margin of the state and the Gulf of Mexico's passive margin began to form. Today {{convert|9|to|12|mi|km|0}} of sediments are buried beneath the Texas continental shelf and a large proportion of remaining US [[oil reserves]] are here. The incipient Gulf of Mexico basin was restricted and seawater often evaporated completely to form thick [[evaporite]] deposits of Jurassic age. These salt deposits formed [[salt dome]] [[diapir]]s, and are found in East Texas along the Gulf coast.<ref name="DiaperGrowth">{{cite conference |last=Muzzafar |first=Asif |title=Timing of Diapir Growth and Cap Rock Formation, Davis Hill Salt Dome, Coastal Texas |url=https://gsa.confex.com/gsa/2001AM/finalprogram/abstract_24852.htm |conference=GSA Annual Meeting, November 5–8, 2001 |publisher=The Geological Society of America |access-date=July 22, 2008 |archive-url=https://web.archive.org/web/20080907164932/http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_24852.htm |archive-date=September 7, 2008 |url-status=dead}}</ref>

East Texas outcrops consist of [[Cretaceous]] and [[Paleogene]] sediments which contain important deposits of [[Eocene]] [[lignite]]. The Mississippian and Pennsylvanian sediments in the north; Permian sediments in the west; and Cretaceous sediments in the east, along the Gulf coast and out on the Texas [[continental shelf]] contain oil. [[Oligocene]] [[volcanic]] rocks are found in far west Texas in the [[Big Bend, Texas|Big Bend]] area. A blanket of [[Miocene]] sediments known as the [[Ogallala Aquifer|Ogallala formation]] in the western high plains region is an important [[aquifer]].<ref name="Ogallala">{{cite web |url=http://www.npwd.org/new_page_2.htm |title=Ogallala Aquifer |access-date=July 23, 2008 |publisher=North Plains Groundwater Conservation District |archive-url=https://web.archive.org/web/20080704071707/http://www.npwd.org/new_page_2.htm |archive-date=July 4, 2008 |url-status=dead}}</ref> Located far from an active [[plate tectonic]] boundary, Texas has no [[volcanoes]] and few earthquakes.<ref name="earthquakes">{{cite web |url=https://www.ig.utexas.edu/research/projects/eq/compendium/earthquakes.htm |title=Earthquakes |access-date=July 23, 2008 |publisher=Jackson School of Geosciences—University of Texas |archive-url=https://web.archive.org/web/20080501011850/http://www.ig.utexas.edu/research/projects/eq/compendium/earthquakes.htm |archive-date=May 1, 2008}}</ref>