It was declared a National Natural Landmark in June 1971 for its excellent example of karst topography and underground stream piracy.

By the process of stream piracy, the smaller Saint Louis River, which runs to Lake Superior, captured the Cloquet and most of its drainage basin.

In so doing, it captured the flow of the upper Eel, a classic example of stream piracy that shifted Cedar Creek's drainage (about 175,000 acres) from the Eel-Wabash system to that of the St. Joseph-Maumee.

Stream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream.

Cutting through the north limb of the Wabash Moraine, a debris deposit left by the retreating ice, the discharge left a large outwash fan that blocked the Eel, diverting its upper portion into the canyon in a classic example of stream piracy that formed today's Cedar Creek.