The opening of the canyon near Shoshone starts of in the Precambrian era nearly a billion years ago. The canyon ends in the Permian 250 million years ago. Nearly every geologic layer in the interim, covering the evolution of animal and plant life, is visible indexed like a library. When you exit the canyon toward Thermopolis, you enter the bright red sandstone and shales of the Triassic, when dinosaurs first began to evolve. Thermopolis itself is covered in the Jurassic and Cretaceous, the peak of dinosaurs. This area is famous for textbook geology.