The geologic history of Boulder County’s remarkable landscape goes back nearly two billion years! Rocks contain a record of the earth’s history that can be read like the pages in a book. Join volunteer naturalists for this slide program and learn how to read this fascinating story in the rocks. Registration required. Register Registration is required through Discover Boulder County, Parks & Open Space’s volunteer and event registration system. If you’re new to the system, you'll need to create an account. But it’s easy and we only use your contact information to communicate about events you register for. We will never sell or give your information to a third party.