Large national parks, established in the early 1900s, have provided a continuing source of revenue; tourism has grown steadily. During World War I the price of silver soared again and the economy prospered. The stock-market crash of 1929 and the droughts of 1935 and 1937 brought hardships, but the economy recovered again during World War II, when the state’s foods, minerals, and metal products were important to the war effort.

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.

While Colorado was seeking to establish a government and engaged in conflict with Native Americans, the state’s mining boom was in sharp decline. The surface gold had been extracted in the middle 1860s, and mining areas became, and in many cases remain, studded with ghost towns—machinery abandoned and shacks deserted. Other towns, such as Central City with its famous opera house dating from the city’s days of opulence, managed to stay alive.

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.