Iowa City: engineers and fossils

The two Iowa City landmarks that are rated highest by users of some travel websites are the University of Iowa campus and the Devonian Fossil Gorge. I'd never heard of the gorge though, as it turns out, it was created by the 1993 flood about which Rachel had told me vivid stories. The U.S. Army Corps of Engineers, which manages the site, apparently has nothing about it on its website so here's a summary with photos by a local TV meteorologist.

After stopping at the visitor center on Prairie du Chien Road (actually in Newport north of Iowa City, so poor Kathy the GPS struck out once again through no fault of her own) I walked across the Coralville Dam, built on the Iowa River in 1958 by the Corps of Engineers for flood control. Coralville Lake on the right (upstream) side of the dam in this photo is the reservoir created by the dam.

I stopped partway across to admire the large flock of turkey vultures that I later learned spends every summer here. My sudden appearance had disturbed the ones you see in flight here, but once they got used to me they just sat there looking like vultures, with tiny naked red heads atop large bodies about a foot and a half long.

This photo looking downstream from the dam also shows the same minor flooding that I showed you yesterday near downtown Iowa City, farther downstream.

Beyond the dam of piled rocks is a lower concrete structure, the emergency spillway, designed to release excess water during a major flood to protect the main dam. In this photo from below the dam, the spillway is at the left. It has worked so far, and that's where the story of the Devonian Fossil Gorge begins.

In the massive June 1993 flood, water in the reservoir rose dozens of feet. At its peak a five foot-high torrent flowed over the emergency spillway, sweeping away a road, campground, 17 feet of topsoil, and huge boulders from the underlying layers of limestone before rejoining the main river channel downstream and flooding Iowa City and other areas. The Corps of Engineers points out that the damage would have been far worse without the dam.

When the floodwater finally receded in August it revealed the scene you see above: layer upon layer of limestone. Word spread that the rocks were full of fossils from the Devonian (416-359 million years ago), when a warm shallow sea somewhat like the Caribbean covered central North America. Geologists and then tourists came flocking; one tourist website still says it's OK to help yourself to any fossils you find (not true). Most of the fossils aren't spectacular anyway; this close-up shows a lot of rings and sticks that are apparently the scattered remains of extinct crinoids, related to starfish (a few kinds still live today).

A new flood in 2008 swept away 15 years' accumulation of weeds and soil - and all the signs interpreting the fossil record for visitors, which the visitor center staff says will eventually be replaced. It also moved more rocks and uncovered more fossils.

By the time I finished exploring the gorge and taking dozens of photos it was starting to rain. I went back for Penny the Prius to continue exploring, but as I drove by the gorge I saw a doe cross the road and pause to find a path down the gorge wall. By the time I parked and walked back to where I had a clear view, she and a companion had crossed and were grazing on the far bank. Sorry that it's blurry - someone must have jostled my elbow even though I had the place to myself as I had all morning.

Finally, since it was still raining, I drove instead of walking to the main river channel to take a photo of the outflow from the dam itself. This flow is regulated to release more water when the reservoir is rising, and as you can see here the effect when the level is high, as now, is dramatic.

After a brief visit to the Coral Ridge Mall west of Iowa City to replace my broken watch (have I mentioned that I hate to shop?) I headed downtown, arriving just as the rain stopped. One of the areas Rachel took me to in 2004 was an X-shaped pedestrian mall near the university campus where College Street (shown here) crosses Dubuque Street. On Dubuque Street I went to Donnelly's Pub; their menu is decidedly not Irish but my fish and chips was excellent.

I rushed back to the motel to share these photos with you but the sun is out and I'm going exploring again. If I end up with more stories or photos I'll put them in a new post so you don't miss them.