Editing Miami (section)

===Geology===
The surface bedrock under the Miami area is called [[Miami oolite]] or Miami limestone. This bedrock is covered by a thin layer of soil, and is no more than {{convert|50|ft|m}} thick. Miami limestone formed as the result of the drastic changes in sea level associated with recent [[glacial period]]s, or [[ice age]]s. Beginning some 130,000 years ago, the [[Sangamonian|Sangamonian Stage]] raised sea levels to approximately {{convert|25|ft|m|0}} above the current level. All of southern Florida was covered by a shallow sea. Several parallel lines of reef formed along the edge of the submerged Florida [[plateau]], stretching from the present Miami area to what is now the [[Dry Tortugas]].<ref name="geology"/>

The area behind this reef line was a large lagoon. Miami limestone formed throughout the area from the deposition of oolites and the shells of [[bryozoans]]. Starting about 100,000 years ago, the [[Wisconsin glaciation]] began lowering sea levels, exposing the floor of the lagoon. By 15,000 years ago, the sea level had dropped {{convert|300|to|350|ft|m|-1}} below the current level. The sea level rose quickly after that, stabilizing at the current level about 4,000 years ago, leaving the [[mainland]] of South Florida just [[Above mean sea level|above sea level]].<ref name="geology">{{Cite web |title=Miami Geology |url=http://www.miami-americabeach.com/about_us/Miami_Geology.html |archive-url=https://web.archive.org/web/20170314102309/http://www.miami-americabeach.com/about_us/Miami_Geology.html |archive-date=March 14, 2017 |access-date=April 3, 2019 |website=miami-americabeach.com}}</ref>

Beneath the plain lies the [[Biscayne Aquifer]], a natural underground source of fresh water that extends from southern [[Palm Beach County, Florida|Palm Beach County]] to [[Florida Bay]]. It comes closest to the surface around the cities of [[Miami Springs, Florida|Miami Springs]] and [[Hialeah, Florida|Hialeah]].<ref>{{Cite web |title=USGS Ground Water Atlas of the United States |url=http://capp.water.usgs.gov/gwa/ch_g/G-text4.html |access-date=February 19, 2006 |publisher=[[United States Geological Survey]] |archive-date=June 16, 2008 |archive-url=https://web.archive.org/web/20080616200409/http://capp.water.usgs.gov/gwa/ch_g/G-text4.html |url-status=live }}</ref> Most of the [[Miami metropolitan area]] obtains its drinking water from the Biscayne Aquifer. As a result of the aquifer, it is not possible to dig more than {{convert|15|to|20|ft|m|abbr=on|0}} beneath the city without hitting water, which impedes underground construction, though some [[Underground parking in South Florida|underground parking garages]] exist. For this reason, the [[rapid transit|mass transit]] systems in and around Miami are elevated or [[land grading|at-grade]].<ref name="geology" />

Most of the western fringes of Miami border the [[Everglades]], a tropical marshland covering most of the southern portion of Florida. [[American alligator|Alligators]] that live in the marshes have ventured into Miami communities and onto major highways.<ref name="geology" />