Geologic Provinces of the United States: Interior Plains gallery

The Green River Valley

Mammoth Caves National Park
Photo by Phil Stoffer, USGS

The Green River has incised into the Pennyroal Plateau, a part of the ancient landscape surface that extended across the entire midwest region prior to the periods of glaciation starting in the Pliocene Epoch (about 5 million years ago).

Trail to Historic Cave Entrance

Mammoth Cave National Park
Photo by Phil Stoffer, USGS

The caprock of the Pennyroyal Plateau in the Mammoth Cave region are sandstone, shale, and conglomeratic beds.

First Creek Trail

Mammoth Cave National Park
Photo by Phil Stoffer, USGS

The Delaware River makes a sweeping bend as it heads throogh the world-famous Delaware Water Gap. The bend of the river mimics the underlying geology.