Editing Saint Anthony Falls (section)

==Geology==
[[Image:Limestone-sandstone.jpg|thumb|right|upright|Sandstone layered under limestone]]
[[Geologist]]s say that the falls first appeared roughly 12,000 years ago about {{convert|10|mi}} downstream at the confluence of the [[glacial River Warren]] (at present-day [[Fort Snelling]]).<ref name="corp" /> Estimates are that the falls were about {{convert|180|ft|m}} high when the [[River Warren Falls]] receded past the confluence of the Mississippi River and the glacial River Warren. Over the succeeding 10,000 years, the falls moved upstream to its present location. The water churning at the bottom of the falls ate away at the soft [[sandstone]], eventually breaking off the hard [[limestone]] cap in chunks as the falls receded. From its origins near Fort Snelling, St. Anthony Falls relocated upstream at a rate of about {{convert|4|ft|m}} per year until it reached its present location in the early 19th century. In the 6 miles (9.7&nbsp;km) from the top of the falls (not including the horseshoe dam) to below the Ford dam the river drops 97 feet (30 m), all of it the remnant of the original 180 feet (55 m) falls. The limestone cap gets thinner upriver from the falls, and the cap disappears about {{convert| 1,200|ft|m}} upstream. In a short time, geologically speaking, the falls will reach the end of the cap and become a rapids.<ref name="corp" />
{{sfn|Feasibility|1984|p=133}} Tributaries such as [[Minnehaha Creek]] begot their own waterfalls as the Mississippi River valley was cut into the landscape.<ref>The river previously split, with two channels around an island where the Minnesota Veterans Home now is. Falls on the east channel progressed faster and cut off the west channel. Minnehaha falls has cut upstream about {{convert|600|ft|m}} from the west channel.</ref>

When Father Louis Hennepin documented the falls he estimated the falls' height to be {{Convert|50 to 60|ft}}. Later explorers described it as being in the range of {{Convert|16 to 20|ft}} high.<ref name=corp/> The height of the falls, not including the upper dam, is now {{convert|35|ft|m}}. The river descends downstream from the falls, which might add another {{convert|10|ft|m}} to the falls where they were when Hennepin saw them.

The geological formation of the area consisted of a hard thin layer of [[Platteville Limestone|Platteville Formation]], a [[limestone]], overlaying the soft [[St. Peter Sandstone]] subsurface.<ref>{{cite web |title=A history of the St Anthony falls |url=http://www.esci.umn.edu/courses/1001/1001_kirkby/SAFL/WEBSITEPAGES/0.html |publisher=University of Minnesota |archive-url=https://web.archive.org/web/20150502031848/http://www.esci.umn.edu/courses/1001/1001_kirkby/SAFL/WEBSITEPAGES/0.html |access-date=July 20, 2021|archive-date=2015-05-02 }}
Multiple sections can be linked through the menu at top right.</ref> These layers were the result of an [[Ordovician Period]] sea which covered east-central Minnesota 500 million years ago.<ref name = FSTS>{{cite web| last = Anfinson| first = Scott| title = Archaeology of the central minneapolis riverfront| publisher = The Institute for Minnesota Archaeology| year = 1989| url = http://www.fromsitetostory.org/sources/papers/mnarch48/48hist.asp| access-date = 2007-05-08}}</ref>