Ohio's geology provides many opportunities for collecting rocks, minerals, and fossils. Most specimens are collected from exposures of the firm bedrock, both natural and human-made, but other specimens distributed around the state were deposited by large continental ice sheets that covered parts of the state during Ohio's Ice Age. Amateur collecting of geological specimens is a fun, educational hobby for many Ohioans.
At least 55 mineral species are known from Ohio and interesting rocks include colorful flint, glacial erratics, and septarian concretions. Small quantities of gold have been collected from glacial deposits. The state abounds with Paleozoic Era fossils, both marine and terrestrial, and scattered Pleistocene (Ice Age) deposits have yielded a variety of plant and animal fossils, including skeletons of large extinct mammals such as mastodons, mammoths, giant ground sloths, and giant beavers.