Shades State Park: A Missing Part of the Geologic Story (GM-33)
Trail I, following a niche high on the canyon wall, passes just beneath a bluff of sandstone. Rocks exposed here reveal an irregular surface of contact between sandstone above and siltstone below. The sandstone was formed during the Pennsylvanian Period about 235 million years ago; the siltstone, Mississippian in age, is about 250 million years old. The surface between them, called an unconformity, represents a gap of about 15 million years in geologic time. It tells of a period of erosion separating the deposition of the rocks above and below. In a few places fragments torn from the older rocks are found where they were redeposited among the younger sediments above.

In other places rocks that fill this gap in the geologic record are present. But at the Shades, it is as if these pages have been torn from the story of the past.

Computer graphics oblique aerial view

Our Hoosier State Beneath Us: Geomorphology