The mining era was launched with the discovery of gold west of Denver in 1859, but by the 1870s silver had taken center stage. Mountain smelter sites, such as Leadville and Aspen, turned into thriving population centers ­almost overnight.

The state relied heavily on its abundant natural resources, and the 20th century was economically topsy-turvy. Tourism and the high-tech industry have come to the rescue and made Colorado the most prosperous of the Rocky Mountain states.

The 1860s saw the most serious conflicts between Native Americans and white settlers in Colorado’s history. To make way for white settlers, the federal government forced Cheyenne and Arapaho off their tribal lands. Left with no alternative, these tribes returned to their nomadic lifestyle. Attacks on towns and travelers were common as the Arapaho and Cheyenne suffered from a government-mandated buffalo extermination program. By depleting their primary source of food, the government hoped to eradicate Native Americans in Colorado.

One of the U.S. government’s most infamous acts against Native Americans occurred in November 1864. Accepting the military’s invitation to camp near Fort Lyon, in southeastern Colorado Territory, Cheyenne and Arapaho set up winter camp and flew the American flag. However, on November 29, nearly 700 U.S. volunteer cavalry attacked the camp, killing and mutilating at least 165 Native Americans, including women and children, in what came to be known as the Sand Creek Massacre.

The Colorado Territory’s boundaries were preserved when, after several unsuccessful attempts, it entered the Union on August 1, 1876, as America’s 38th state. Colorado is nicknamed the Centennial State in honor of the 100th anniversary of the Declaration of Independence.

In the mid-1960s Colorado experienced a large influx of new residents and rapid urban growth and development, especially along a strip (c.150 mi/240 km long) centered on Denver and stretching from Fort Collins and Greeley in the north to Pueblo in the south. This growth, combined with the area’s high altitude, caused pollution problems, most notably smog. The discovery and exploitation of oil created a boom in the 1970s, which collapsed in the early 1980s. Diversifying industry, swelling in-migration and accompanying construction, and tourism and recreation have since enabled Colorado to rebound, and between 1990 and 2000 it had the third largest percentage of growth of any state in the union.

The completion (1870) of a railroad link from Denver to the Union Pacific in Cheyenne, Wyo., and later railroad construction helped to stimulate the extension of farming and the growth of huge cattle ranches as well as to encourage an influx of settlers. Between 1870 and 1880 population increased almost fivefold. Denver briefly became the largest receiving market for sheep, and a smelting industry was established.

In the 1870s the discovery of silver-bearing lead carbonite ore at Leadville started a new mining boom. Prosperity was short-lived, however, for in the 1890s, despite a rich silver strike at Creede and the discovery of the state’s richest gold field at Cripple Creek, Colorado suffered a depression. In 1893 the U.S. government stopped buying silver in order to restore confidence in the nation’s currency, which had been placed on the gold standard in 1873. The silver market subsequently collapsed, dealing a severe blow to Colorado’s economy.

Labor conflicts, disputes over railway franchises, and warfare between sheep and cattle interests also plagued the state at the turn of the century. Many of labor’s battles in this period were fought in the mines of Colorado, and the lawlessness and ruthlessness that prevailed among both employers and miners were reminiscent of the early days of the mining camps. When the silver market broke, Colorado turned politically to fusion Populist-Democratic leaders advocating a return to bimetallism. The free-silver movement, however, was unsuccessful, and by 1910, with the improvement of national economic conditions, Colorado settled down to a predominantly agricultural economy.

At the time of the gold rush the area in which the gold fields were located was part of the U.S. Kansas Territory. A group of miners organized the gold fields as Arapahoe co. of Kansas Territory. The region was divided into districts, and miners’ and people’s courts were set up to provide quick justice. The miners sought separate territorial status in 1859 and formed the illegal Territory of Jefferson, which operated until the bill for territorial status was passed by Congress in 1861. William Gilpin, the first territorial governor, chose the name Colorado . Measures proposing statehood for Colorado were introduced in the U.S. Congress in 1864, and again in 1866 and 1867 when they were vetoed by Andrew Johnson. A bill granting Colorado’s statehood was finally passed by Congress in 1876.

When the first settlers came to Colorado, the Ute lived in the mountain areas, while the Comanche, Cheyenne, Arapaho, and Kiowa inhabited the Great Plains. Warfare between plains and mountain ethnic groups was continuous. The tribes of the plains combined their forces in 1840 to halt the invasion of their homelands and hunting grounds by settlers, and violence ensued. The warfare finally culminated in the Native Americans’ defeat after the Indian Wars (1861–69) and the Buffalo War (1873–74). Colorado’s Native Americans now live mainly on the Southern Ute reservation and in the Denver area.

The first European to enter the region was probably the Spanish conquistador Francisco Vásquez de Coronado in the 16th cent. Spain subsequently claimed (1706) the territory, although no Spanish settlements were established there. Part of the area was also claimed for France as part of the Louisiana Territory. At the end of the French and Indian Wars (1763), France secretly ceded the Louisiana Territory, including much of Colorado, to Spain. The French regained the whole area in 1800 by the secret Treaty of San Ildefonso concluded with Spain (see San Ildefonso, Treaty of).

The United States bought the area of the Arkansas River and E of the Rocky Mts. in the Louisiana Purchase of 1803. The federal government sent expeditions to Colorado which generated some public interest in the new territory, and they explored routes opened earlier by the famous mountain men, trappers, and fur traders who included William H. Ashley, James Bridger, Jedediah S. Smith, Kit Carson, and the Bent brothers. Bent’s Fort, in Colorado, was one of the best-known Western trading posts. Settlement in the area did not begin, however, until the United States acquired the remainder of present-day Colorado from Mexico by the Treaty of Guadalupe Hidalgo in 1848.