In the summer of 1867, with a small party of naturalists, students, and amateurs like myself, I visited the mountain region of Colorado Territory. While in Middle Park, I explored a little cañon, through which the Grand River runs, immediately below the well-known watering-place, "Middle Park Hot Springs." Later in the fall I passed through Cedar Cañon, the gorge by which the Grand leaves the park. The result of the summer's study was to kindle a desire to explore the cañons of the Grand, Green, and Colorado Rivers, and the next summer I organized an expedition with the intention of penetrating still farther into that cañon country.