One of the most remarkable aspects of the Upper Peninsula as a whole and CLT in particular is the stunning amount of rock left behind in the retreat of glaciers at the end of the last Ice Age. The Cisco Branch basin is tangible proof of this retreat. Giant boulders are prominent up and down the river, while the rocky riverbed provides a colorful diversity of stone. In fact, the cabin sits on what has been determined to be the oldest rock in the United States, at 3.6B to 3.8B years old