In Hidden Thunder, renowned watercolor artist Geri Schrab and archaeologist Robert "Ernie" Boszhardt give readers an up-close-and-personal look at rock art. With an eye toward preservation, Schrab and Boszhardt take you with them as they research, document, and interpret at the ancient petroglyphs and pictographs made my Native Americans in past millennia. In addition to publicly accessible sites such as Wisconsin’s Roche-a-Cri State Park and Minnesota’s Jeffers Petroglyphs, H...