For the past few summers, I have led geology tours around the Twin Cities for community education courses. The tours usually involve features such as caves, springs, and waterfalls. One of the big local geology stories is the upstream retreat of the waterfalls at the end of the last ice age, when great torrents of water from the melting glaciers to the north spilled through the metro area in volumes not seen before or since. One night not long ago, as I was sleeping, I had a most unusual dream about this part of our local heritage.
Imagine standing on the brink of Niagara Falls. That’s about what downtown Saint Paul must have looked like at the end of the last Ice Age, if you were looking into the Mississippi River gorge from about where City Hall stands today. Except that Saint Paul’s waterfall was even larger. Geologists refer to this waterfall as the Glacial River Warren Falls, named for the Civil War general G. K. Warren, “the hero of Little Round Top” at the Battle of Gettysburg, who was also a military engineer and wrote of our local topography. The waterfall began near what is now the Robert Street Bridge, but the torrential churning undercut the waterfall’s limestone ledge, hollowing out caverns in the softer sandstone below, causing the ledge to collapse repeatedly, so that the waterfall migrated upriver over thousands of years. About ten thousand years ago, upon reaching what is now Fort Snelling, a smaller waterfall, St. Anthony Falls, branched off, and began its own migration upriver to its present location in Minneapolis, where it was stabilized by the Corps of Engineers beginning in the 1870s. But Saint Paul’s great waterfall exists no more—having departed the city limits, it disintegrated into a series of rapids along the Minnesota River. There’s a nice painting of this primeval waterfall at the Science Museum of Minnesota in Saint Paul, together with some of the extinct megafauna, like giant beavers, that graced the forlorn landscape.
Those are the facts; now for my dream. In my dream, I saw the sweeping four-thousand-foot-wide crescent of the Glacial River Warren waterfall arrayed before me like a steel-gray curtain enveloped in mist. The dream continued as I explored a series of caverns behind and underneath the mighty waterfall, the entire scene illuminated by flaming torches. The thundering reverberations of the cataract shook the ground. I recall being amazed at the complexity and intricacy of these caverns, how they wound about behind the curling sheet of water. And that was all—I was woken up by my cats, but otherwise I probably would not have remembered the dream in the first place.
Archeologists have documented the presence of Native Americans in Minnesota as far back as twelve thousand years ago, during the time when Saint Paul’s great waterfall was in existence, so it’s at least possible that such romantic, torch-lit scenes indeed played themselves out millennia ago. But we have no way of knowing for sure, because the waterfall caverns themselves—more likely a series of caverns over thousands of years—were of course successively created and destroyed as the waterfall migrated upstream. No trace of them remains today; they have vanished like a dream.