Which natural formation is iconic in the Sleeping Bear Dunes National Lakeshore?

The iconic natural formation in the Sleeping Bear Dunes National Lakeshore is indeed the towering sand dunes. This area is renowned for its dramatic landscapes, which include some of the tallest sand dunes in the United States, rising up to 450 feet above Lake Michigan. The dunes are not only impressive due to their height but also because they are part of a dynamic ecosystem shaped by wind and waves. The impressive vistas provided by these dunes attract many visitors, offering unique opportunities for hiking, photography, and scenic overlooks of the surrounding landscape.

Additionally, the dunes are a significant part of the area's natural heritage and contribute to its environmental diversity. They serve as a habitat for various plant and animal species, which is essential to the ecological balance of the region.

The other choices, while important to Michigan's landscape, do not hold the same iconic status within Sleeping Bear Dunes National Lakeshore. The Lake Superior shoreline, the Great Lakes, and the Crystal River are all beautiful and significant in their own right, but the towering sand dunes are the defining characteristic that makes this national lakeshore unique and recognizable.