I would love to see someone map out, just like what Ryan Thompson has done with Geneva's, all the glacial erratics in Chicago, its immediate environs and not-too-further afield, at least the more monumental ones, and if there are any to be found, as a sort of field guide to the city's ancestral (and far-future) landscape, intriguing hints at the primordial forces that shaped (and even today continue to influence) its urban history.
That, or build !melk et alia's rejected artificial glacier for Navy Pier.
POSTSCRIPT #1: See Jane Hutton's Distributed Evidence: Mapping Named Erratics in Making the Geologic Now:
This project maps a series of boulders that were plucked, transported, and deposited by the toe-line of the retreating Late-Wisconsin and pre-Wisconsin ice sheets in North America and subsequently named, relocated, modified, and celebrated by people. They are the glacially distributed sites of council meetings, picnics, political movements, and territorial markers. They are inscribed with discrepant personal, regional, and national narratives and at the same time they declare their foreign origin through their conspicuous mineral composition and form.
There's also this video of Hutton discussing her research at the Geologic Turn symposium at Taubman College on February 2012.