Rivers and streams

...but we must remember that the river cut its way through a region that was slowly rising above the level of the sea, and the rain washed out the valleys, and left rocks and cliffs standing, and the river never turned aside from its original course to seek an easier way, for the process of uplift was not greater than that of corrasion.

Exploration of the Colorado River of the West and its tributaries.: Explored in 1869, 1870, 1871, and 1872, under the direction of the secretary of the Smithsonian institution.