The state was named for the Colorado River, which Spanish travelers named the Río Colorado for the ruddy (Spanish: colorado) silt the river carried from the mountains. The Territory of Colorado was organized on February 28, 1861, and on August 1, 1876, U.S. President Ulysses S. Grant signed a proclamation admitting Colorado to the Union as the 38th state. Colorado is nicknamed the "Centennial State" because it became a state 28 days after the centennial of the United States Declaration of Independence.