Earlier this week, I had occasion to take a ranger-guided tour of the historic Coldwater Spring site near Fort Snelling. The last time I had visited this place, considered sacred by many American Indians, the dozen abandoned buildings once operated by the U.S. Bureau of Mines were still standing. They were still there on Wednesday, but they - and a few parking lots - had been converted into the 13,000 cubic yards of crushed concrete you can see above.

The National Park Service has demolished the buildings as part of its project to restore the 27-acre site to an oak savanna/tall grass prairie environment. The more natural-looking landscape perhaps will make it easier for visitors to imagine the crucial role that the spring played in the 19th century history of Minnesota. Except for the tours, the site is closed to the public. Our guides told us that the park service is trying to recycle as much of the demolition debris as they can - the heaps of fine rubble could be tomorrow's roadbed.