Skirting the Bighorns and extending into Colorado and Montana is the vivid red Chugwater formation. An enormous pile of silt and sandstone it dates back to the Triassic period (245 to 208 million years ago), basically to the dawn of the dinosaurs. Photographed, here, not far from the “Hole-in-the Wall” hideout of Butch Cassidy and Sundance Kid, near Barnum, WY