In Ohio, nearly 500 million years are recorded in sedimentary bedrock laid down on the floors of ancient seas that periodically inundated the state, preserving evidence of inland seas, mountain upheaval, vast swamps, and changing conditions over immense spans of time. Sandstone, shale, and limestone formed from different sediments and marine environments, while eastern Ohio’s coal measures developed as seas repeatedly advanced and withdrew, killing swamp vegetation with salt water and burying it beneath sand and mud. These rock layers, oldest at the bottom, dip slightly in the southeast and northwest and are fairly level from Cincinnati north to Toledo, forming a broad arch that exposes older strata at its center and younger layers toward the southeast and northwest. Little Beaver Creek cuts through 300 million year old bedrock from the Pennsylvania period, where alternating marine and swamp deposits reflect rising and falling seas. The area also preserves evidence of the Pleistocene Ice Age, including older Illinoian deposits extending south beyond the later Wisconsinan deposits. South of the park, ridges stretch toward the mountains as part of the Appalachian plateau, where uplifted but mostly level bedrock has been deeply cut by streams, preserving the worn remains of ancient mountains in sandstone and shale.