Geology of Starved Rock – How these amazing canyons came to be

Starved Rock State Park, an amazing area complete with hiking trails and waterfalls is located in Deerpark Township and LaSalle Counties in Illinois, sits along the south bank of the Illinois River.  

Starved Rock is famous for its fascinating rock formations, which are mainly outcrops of St. Peter Sandstone.  This sandstone began as a sheet of sand in clear, shallow water near the shore of a Paleozoic sea and consists of fine-to-medium-size, well-rounded quartz grains with frosted surfaces. The extent of these amazing formation span north–south from Minnesota to Arkansas and east–west from Illinois into Nebraska and South Dakota.

This sandstone is an Ordovician geological formation. This sandstone originated as a sheet of sand in clear, shallow water near the shore of a Paleozoic sea and consists of fine-to-medium-size, well-rounded quartz grains with frosted surfaces. The extent of the formation spans north–south from Minnesota to Arkansas and east–west from Illinois into Nebraska and South Dakota.

The sandstone, typically buried, is exposed in this area due to an anticline, a convex fold in underlying strata. This creates canyons and cliffs when streams cut across the anticline. The sandstone is pure and poorly cemented, making it workable with a pick or shovel.  A similar geologic feature is found at  Castle Rock State Park, also in Illinois.

What helped create the park’s signature geology and features was 1 catastrophic flood known as the Kankakee Torrent, which took place somewhere between 14,000 and 17,000 years ago.

This flood, the  Kankakee Torrent  resulted from a breach of moraines forming a large glacial lake fed by the melting of the Late Wisconsin Laurentide Ice Sheet. The point of origin of the flood was Lake Chicago. The landscape south of Chicago still shows the effects of the torrent, particularly at Kankakee River State Park and on the Illinois River at Starved Rock State Park which took place somewhere between 14,000  and 17,000 years ago, before humans occupied the area, helped create the park’s signature geology and features, which are very unusual for the central plains.

The park is on the south bank of the Illinois River.

The Hennepin Canal roughly follows the ancient channel of the Mississippi upstream of Rock Island.), a major tributary of the Mississippi River, between the Fox and Vermilion Rivers. The Vermilion created large sandbars at the junction of the Illinois, preventing practical navigation farther upriver. Rapids were found at the base of the butte before the construction of the Starved Rock Lock and Dam.

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Aerial Geology

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