Near Iowa City in Johnson County, Iowa — The American Midwest (Upper Plains)

An Ancient Sea

Photographed By Connor Olson, July 25, 2020

1. An Ancient Sea Marker

Inscription. Click to hear the inscription.

Although the huge 1993 increase in water flow changed the landscape at the Dam site and caused flooding downstream, catastrophic flooding was avoided. The Iowa River returned to normal flow over the next few months, and the Dam itself remained structurally sound. By August, a by- product of the event appeared as the waters receded. The flood had opened a window to Earth's ancient geologic past. The scoured rock surfaces below the Spillway revealed clear evidence of the shallow tropical seas that existed here 375 million years ago, during the Devonian Period.

Topics. This historical marker is listed in these topic lists: Anthropology & Archaeology • Disasters • Waterways & Vessels. A significant historical year for this entry is 1993.

Location. 41° 43.303′ N, 91° 31.932′ W. Marker is near Iowa City, Iowa, in Johnson County. Marker is on Prairie Du Chien Road Northeast. Touch for map. Marker is at or near this postal address: 2850 Prairie Du Chien Rd NE, Iowa City IA 52240, United States of America. Touch for directions.

Other nearby markers. At least 8 other markers are within 4 miles of this marker, measured as the crow flies. The Coralville Dam (here, next to this marker); Devonian Fossils (a few

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steps from this marker); View from the Overlook Plaza (a few steps from this marker); Site Geology (a few steps from this marker); Samuel Jordan Kirkwood (approx. 3.8 miles away); Old Brick (approx. 4 miles away); Mormon Handcart Brigade Camp (approx. 4.1 miles away); St. Mary's Church (approx. 4.1 miles away). Touch for a list and map of all markers in Iowa City.

Photographed By Connor Olson, July 25, 2020

2. An Ancient Sea Marker

Credits. This page was last revised on June 7, 2021. It was originally submitted on June 6, 2021, by Connor Olson of Kewaskum, Wisconsin. This page has been viewed 125 times since then and 36 times this year. Photos: 1, 2. submitted on June 6, 2021, by Connor Olson of Kewaskum, Wisconsin. • Mark Hilton was the editor who published this page.