Colorado is a U.S. state that encompasses most of the Southern Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains. Colorado is part of the Western United States, the Mountain States, and the Southwestern United States.The state was named for the Colorado River, which early Spanish explorers named the Rio Colorado for the red colored (Spanish: Colorado) silt the river carried from the mountains. In 1861, Jefferson Territorial officials decided that "Colorado" would be a fitting name for a new territory. Colorado is nicknamed the "Centennial State" because it was admitted to the Union as the 38th state in 1876, the centennial year of the United States Declaration of Independence.

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