Colorado is a landlocked state in the Mountain West subregion of the Western United States. It is part of the Southwestern United States, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas to the east, and Oklahoma to the southeast. Colorado is noted for its landscape of mountains, forests, high plains, mesas, canyons, plateaus, rivers, and desert lands. It 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 the eighth-largest U.S. state by area and the 20th by population. The United States Census Bureau estimated the population of Colorado to be 5,957,493 as of July 1, 2024, a 3.2% increase from the 2020 United States census.
The region has been inhabited by Native Americans and their Paleo-Indian ancestors for at least 13,500 years and possibly much longer. The eastern edge of the Rocky Mountains was a major migration route for early peoples who spread throughout the Americas. In 1848, much of the Nuevo México region was annexed to the United States with the Treaty of Guadalupe Hidalgo. The Pike's Peak Gold Rush of 1858–1862 created an influx of settlers. On February 28, 1861, U.S. president James Buchanan signed an act creating the Territory of Colorado, and on August 1, 1876, president Ulysses S. Grant signed Proclamation 230, admitting Colorado to the Union as the 38th state.
Denver is the capital, the most populous city, and the center of the Front Range Urban Corridor. Colorado Springs is the second-most populous city of the state. Residents of the state are known as Coloradans, although the antiquated "Coloradoan" is occasionally used. Colorado generally ranks as one of the top U.S. states for education attainment, employment, and healthcare quality. Major parts of its economy include government and defense, mining, agriculture, tourism, and manufacturing. With increasing temperatures and decreasing water availability, Colorado's agriculture, forestry, and tourism economies are expected to be heavily affected by climate change.
The region that is today the State of Colorado has been inhabited by Native Americans and their Paleo-Indian ancestors for at least 13,500 years and possibly more than 37,000 years. The Lindenmeier site contains artifacts dating from approximately 8720 BCE. The Ancient Pueblo peoples lived in the valleys and mesas of the Colorado Plateau in far southwestern Colorado. The Ute Nation inhabited the mountain valleys of the Southern Rocky Mountains and the Western Rocky Mountains, even as far east as the Front Range of the present day. The Apache and the Comanche also inhabited the Eastern and Southeastern parts of the state. In the 17th century, the Arapaho and Cheyenne moved west from the Great Lakes region to hunt across the High Plains of Colorado and Wyoming.
The U.S. acquired the territorial claim to the eastern Rocky Mountains with the Louisiana Purchase from France in 1803. In 1806, Zebulon Pike led a U.S. Army reconnaissance expedition into the disputed region. Colonel Pike and his troops were arrested by Spanish cavalrymen in the San Luis Valley the following February, taken to Chihuahua, and expelled from Mexico the following July.
Under the 1819 Adams-Onís Treaty, the U.S. acquired Florida from Spain while relinquishing claims to lands west of the 100th meridian and south of both the Arkansas River and the 42nd parallel. The treaty took effect on February 22, 1821. Having settled its border with Spain, the U.S. admitted the southeastern portion of the Territory of Missouri to the Union as the state of Missouri on August 10, 1821. The remainder of Missouri Territory, including what would become northeastern Colorado, became an unorganized territory and remained so for 33 years over the question of slavery. After 11 years of war, Spain finally recognized the independence of Mexico with the Treaty of Córdoba signed on August 24, 1821. Mexico eventually ratified the Adams–Onís Treaty in 1831. The Texian Revolt of 1835–36 fomented a dispute between the U.S. and Mexico which eventually erupted into the Mexican–American War in 1846. Mexico surrendered its northern territory to the U.S. with the Treaty of Guadalupe Hidalgo after the war in 1848; this included much of the western and southern areas of Colorado.
The Santa Fe Trail connected the Missouri River to Santa Fe, New Mexico, where it linked with the Camino Real de Tierra Adentro extending southward into Mexico. Others traveling overland avoided the rugged Southern Rocky Mountains, and instead followed the North Platte River and Sweetwater River to South Pass (Wyoming), the lowest crossing of the Continental Divide between the Southern Rocky Mountains and the Central Rocky Mountains. In 1849, the Mormons of the Salt Lake Valley organized the extralegal State of Deseret, claiming the entire Great Basin and all lands drained by the rivers Green, Grand, and Colorado. The federal government of the U.S. flatly refused to recognize the new Mormon government because it was theocratic and sanctioned plural marriage. Instead, the Compromise of 1850 divided the Mexican Cession and the northwestern claims of Texas into a new state and two new territories, the state of California, the Territory of New Mexico, and the Territory of Utah. On April 9, 1851, Hispano settlers from the area of Taos settled the village of San Luis, then in the New Mexico Territory, as Colorado's first permanent Euro-American settlement, further cementing the traditions of New Mexican cuisine and New Mexico music in the developing Southern Rocky Mountain Front.
In 1861 following the beginning of the American Civil War, there were several small disputes and skirmishes between confederate supporters and union supporters. In August, Governor Gilpin organized the 1st Colorado Infantry. John P. Slough led the group to New Mexico Territory in February–March 1862. There they fought in the battles of Apache Canyon, Glorieta Pass and Peralta. Slough resigned in April 1862 and was replaced by Major John M. Chivington.
With resources tied up in the war there was little left over for mines, farms, and infrastructure, and Denver stagnated.
On March 26, 1862 John Evans was appointed by Abraham Lincoln as the second governor of the territory. He prompted investment in Denver rail projects, and founded the University of Denver in 1864.
Anti-native sentiment grew during the Civil War years. Exterminationist ideology, led in Colorado by Evans and Chivington, advocated for the total eradication of all native people in the territory. The Colorado War worsened relations with natives until 1864 when Chivington ordered the Sand Creek Massacre and Evans was forced to resign the following spring.
In 1867, the Union Pacific Railroad laid its tracks west to Weir, now Julesburg, in the northeast corner of the Territory. The Union Pacific linked up with the Central Pacific Railroad at Promontory Summit, Utah, on May 10, 1869, to form the First transcontinental railroad. The Denver Pacific Railway reached Denver in June of the following year, and the Kansas Pacific arrived two months later to forge the second line across the continent.
The United States Congress passed an enabling act on March 3, 1875, specifying the requirements for the Territory of Colorado to become a state. On August 1, 1876 (four weeks after the Centennial of the United States), U.S. President Ulysses S. Grant signed a proclamation admitting Colorado to the Union as the 38th state and earning it the moniker "Centennial State".
The discovery of a major silver lode near Leadville in 1878 triggered the Colorado Silver Boom. The Sherman Silver Purchase Act of 1890 invigorated silver mining, and Colorado's last, but greatest, gold strike at Cripple Creek a few months later lured a new generation of gold seekers. Colorado women were granted the right to vote on November 7, 1893, making Colorado the second state to grant universal suffrage and the first one by a popular vote (of Colorado men). The repeal of the Sherman Silver Purchase Act in 1893 led to a staggering collapse of the mining and agricultural economy of Colorado, but the state slowly and steadily recovered. Between the 1880s and 1930s, Denver's floriculture industry developed into a major industry in Colorado. This period became known locally as the Carnation Gold Rush.