![]() ![]() This surrounding area is hilly and higher than the Chicago Plain. Farther inland, a series of moraines surrounds the Chicago Plain. ![]() The greatest example of these can be seen at Indiana Dunes National Park, where some dunes reach up to almost 200 feet. In contrast, south of the city of Chicago into Northwest Indiana it is without bluffs, but instead has sand dunes. North of the city of Chicago, there are steep bluffs and ravines that run along Lake Michigan. Thus, the paradox of Chicago's development as a city in the 19th century became taking advantage of this geography, but also overcoming its limitations. Indeed, Chicago's low lying geography, which ultimately became crucial to its boom town development (as the site of the Chicago Portage and canal), could not initially attract substantial early settlement because the tall grass prairie around its lake and river systems was underlain by hard packed glacial clay, making much of the area forbidding wetlands. When the city we know today was initially founded in the 1830s, the land was swampy and most of the early building began on low dunes around the Chicago River's mouth. During heavy periods of rain or when the Des Plaines overflowed its banks due to downstream ice dams in the early spring, the river would flow through Mud Lake to the South Branch of the Chicago River, forming a favorite portage for early traders and creating the path of the future I&M and Chicago Sanitary and Ship Canals. One special feature of the Chicago area was the now-vanished Mud Lake in the Des Plaines River watershed. ![]() On the North side, the diagonals Clark Street and Ridge Boulevard run along ridges that were once sandbars in the Lake. In fact, it and the nearby Stony Island were both islands in Lake Chicago as it receded. In pioneer days, this hill was called Blue Island, so named because at a distance it looked like an island set in a trackless prairie sea. This plain has very little topographical relief in fact, topographical relief is so unusual in the plain that what would be unnoticed hills and ridges in other locales have been given names. The city of Chicago itself sits on the Chicago Plain, a flat plain that was once the bottom of ancestral Lake Chicago. Chicago's present natural geography is a result of the large glaciers of the Ice Age, namely the Wisconsinan Glaciation that carved out the modern basin of Lake Michigan (which formed from the glacier's meltwater). ![]()
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