Grey Cloud Dunes SNA
The landscape at Grey Cloud Dunes grandly illustrates the story of the Mississippi River's past. Two terraces roughly 50 and 110 feet above the present-day water surface are the handiwork of Glacial River Warren, which drained Glacial Lake Agassiz between 12,000 and 10,000 ago. Atop the terraces are dunes that formed later, during a mid-Holocene warm/dry period 8,000–4,000 years ago, when wind-driven sands from Grey Cloud Island were deposited on the slopes above.