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, Hidden Thunder covers the artistic treasures found at several remote and inaccessible rock art sites—revealing the ancient stories through words, full-color photographs, and artistic renditions.

Offering the duo perspectives of scientist and artist, Boszhardt shares the facts that archaeologists have been able to establish about these important artifacts of our early history, while Schrab offers the artist's experience, describing her emotional and creative response upon encountering and painting these sites. Viewpoints by members of the Menominee, Ho-Chunk, Ojibwe, and other Native nations offer additional insight on the historic and cultural significance of these sites. Together these myriad voices reveal layers of meaning and cultural context that emphasize why these fragile resources—often marred by human graffiti and mishandling or damage from the elements—need to be preserved.