MAP DETAIL from
"Map Showing the Thickness and Character of Quaternary Sediments in the Glaciated United States East of the Rocky Mountains"
U.S. Geological Survey Miscellaneous Investigations Series Map I-1970
1993-1998
by David R. Soller
The glacial deposits across the U.S. Midcontinent are mantled by silty deposits known as loess, which contribute to the high agricultural productivity of the region. Loess formed during the glacier's retreat, as strong winds near the ice margin eroded and deposited the finer-grained sediment. These images show the Missouri River and adjacent areas near Sioux City, IO, where the loess mantle is more than 25' thick (striped areas). There, loess was blown from the River channel, and covers glacial till on the uplands.
