The Indiana Dunes National Lakeshore represents a unique ecological history beginning with the retreat of the last great continental glacier approximately 14,000 years ago. The park currently consists of 15,000 acres spanning 15 miles of Lake Michigan shoreline representing four major successive stages of historic shorelines. Indiana Dunes is one of the most extensive geologic records of the largest complex of freshwater lakes in the world. In the late 1800s several scientific publications had been published featuring the entomology and botany of the Indiana Dunes and in 1916 the National Dunes Association was formed. Public approval for the formation of a National Park was at an all time high; however, the onset of World War I prevented this plan from becoming a reality until 1966.
The area of the park formerly known as the Great Marsh was formed over 4,000 years ago between the Tolleston dunes on the north and the Calumet dunes on the south. This area was an open body of water fed by a single watershed and emptying into Lake Michigan through Dunes Creek. Over time this body of water changed to include conifer swamp, wet prairie, fen, bog, sedge meadow, and marsh. Today, the remaining 205 acres of the Great Marsh stretch only twelve miles with an average width of one-half mile. These collections of wetlands, including Cowles Bog National Landmark, are now known as Cowles Bog Wetland Complex (CBWC).
The CBWC gained recognition in the early 1900s for its unique biodiversity and landscape. It would take Chicago residents a full day of travel to the north to see the same biological diversity they could find by travelling only ninety minutes east to the area then known as Mineral Springs Quaking Bog and Mineral Springs Tamarack Swamp. Its proximity to Chicago made it a highly visited and studied area. Henry Chandler Cowles published a paper in 1899 entitled, “Ecological Relations of the Vegetation on Sand Dunes of Lake Michigan.” For this seminal work, he was later recognized as one of the fathers of plant ecology. The area was first referenced as Cowles Bog in 1923 by Herman Kurz, a student of Henry Cowles at the University of Chicago.