Sipapu Bridge, one of the largest natural bridges in the world, was once also called President and Augusta before those names were changed. William Douglass, leader of the 1908 government survey, had studied Hopi culture extensively in Arizona, and the cliff dwellings and rock art in the area reminded him of it. Charged with finding appropriate Indian names for the bridges, he chose Sipapu, meaning "place of emergence." The bridge formed within Cedar Mesa, a million acre plateau encompassing the monument and surrounding area, made of nearly horizontal sedimentary rock layers. During the Permian Period, wind blown sands from the north and west were deposited here as dunes, then later buried by sediments and transformed over time by pressure and moisture into sandstone, now called the Cedar Mesa Sandstone. After being buried, tilted, and uplifted, the sandstone was slowly exposed by meandering streams that carried away overlying sediments and helped carve Sipapu and the other bridges.