Boulder is a home rule city that is the county seat of, and the most populous municipality in, Boulder County, Colorado, United States. The city is northwest of the Colorado state capital of Denver. Boulder is a college town, hosting the University of Colorado Boulder, the flagship and largest campus of the University of Colorado system, as well as numerous research institutes. Starting in 2027, Boulder will become the new home of the Sundance Film Festival.
History
Archaeological evidence shows that Boulder Valley has been continuously inhabited by Native American tribes for over 13,000 years, beginning in the late Pleistocene era. Throughout the Paleo-Indian, Archaic, and Late Prehistoric periods, indigenous peoples moved seasonally between the mountains and plains, taking shelter in winter along the Front Range trough where Boulder now lies. By the 1500s, the Ute people held primary occupation of Boulder Valley. In the early 1800s, the Arapaho migrated to the region. Additional Native American nations with historical ties to the broader Front Range include the Apache, Arapaho, Cheyenne, Comanche, Kiowa, Pawnee, Shoshone, Sioux, and Ute peoples. In the 1800s, European Americans settled in the area.
Boulder was founded in late 1858 when prospectors led by Thomas Aikins arrived at Boulder Canyon during the Colorado Gold Rush. According to historical accounts, they initially camped in an area historically associated with Arapaho leader Niwot, though the Arapaho's stable settlement had been displaced by earlier treaty obligations. Under the Treaty of Fort Wise (1861), the Arapaho were formally forced to relocate to the Cheyenne-Arapaho Reservation. Some of these early settlers later participated in the 1864 Sand Creek massacre, where Niwot himself was killed. In early 1859, gold was discovered along Boulder Creek, drawing more miners and merchants to the area. The Boulder City Town Company was formed in February 1859 to establish a settlement at the canyon mouth. The Boulder, Nebraska Territory, post office opened on April 22, 1859.
On August 24, 1859, voters of the Pike's Peak mining region approved the formation of the Provisional Government of the Territory of Jefferson, and on November 28, 1859, the extralegal Jefferson Territory created Jackson County with Boulder City as its seat. By 1860, Boulder City had 70 cabins, occupied mainly by Anglo families. Chinese miners and Black residents lived in early Boulder but experienced systematic marginalization and were largely absent from contemporary photographs and official records, reflecting the racial hierarchies of the era. and Boulder County was created on November 1, 1861, with Boulder City as its seat. The Arapaho were forced to relocate by the Treaty of Fort Wise. With declining numbers, Niwot's band soon moved to the Cheyenne-Arapaho Reservation. By 1862, the creek had yielded $100,000 in gold, and Boulder's population exceeded 300.
On November 7, 1861, the Colorado General Assembly passed legislation to locate the University of Colorado in Boulder. The City of Boulder City was incorporated on November 4, 1871. and the university officially opened on September 5, 1877. The City of Boulder City shortened its name to the City of Boulder.
In 1907, Boulder adopted an anti-saloon ordinance. In 1916, statewide prohibition started in Colorado, and ended with the repeal of national prohibition in 1933.
Housing
Median home prices rose 60% from 2010 to 2015 to $648,200. In 2024, the City Council of Boulder repealed a long-standing law that prevented Boulder from increasing new residential units by more than 1% in a year.
In 1959, city voters approved the "Blue Line" city-charter amendment, which restricted city water service to altitudes below , to protect the mountain backdrop from development. In 1967, city voters approved a dedicated sales tax to acquire open space to contain urban sprawl. In 1970, Boulder created a "comprehensive plan" to dictate future zoning, transportation, and urban planning decisions. In 1972, the city enacted a height-limiting ordinance for buildings to preserve views of the Flatirons and surrounding mountains. This ordinance remains in effect and continues to shape Boulder's skyline and downtown development patterns. In 1974, a Historic Preservation Code was passed. In 1976, a residential-growth management ordinance, the Danish Plan, was passed.
Geography
thumb|upright=1.25|Boulder's rock formations, the [[Flatirons]]
The city of Boulder is located in the Boulder Valley, where the Rocky Mountains meet the Great Plains. The Flatirons, slabs of sedimentary stone tilted up on the foothills, are located west of the city and are a widely recognized symbol of Boulder.
Boulder Creek is the primary flow of water through Boulder. The creek was named before the city's founding and its etymology is unknown. It is from Boulder Creek that the city is believed to have taken its name. Boulder Creek has significant water flow, derived primarily from snow melt and minor springs west of the city. The creek flows into St. Vrain Creek east of Longmont, which is a tributary of the South Platte River.
At the 2020 United States census, the city had a total area of , including of water.
Denver International Airport is located east-southeast of Boulder.
Environment
In 1899, government preservation of open space around Boulder began, with the Congress of the United States approving the allocation of of mountain backdrop and watershed extending from South Boulder Creek to Sunshine Canyon.
Wildlife protection
Boulder has created an Urban Wildlife Management Plan which sets policies for managing and protecting urban wildlife. The city's Parks and Recreation and Open Space and Mountain Parks departments have volunteers who monitor parks, including wetlands, lakes, etc., to protect ecosystems. From time to time, parks and hiking trails are closed to conserve or restore ecosystems.
Traditionally, Boulder has avoided using chemical pesticides to control the insect population. However, with the threat of West Nile virus, the city began an integrative plan to control the mosquito population in 2003 that includes chemical pesticides. Residents can opt out of the program by contacting the city and asking that their areas not be sprayed.
Under Boulder law, exterminating prairie dogs requires a permit.
In 2005, the city experimented with using goats for weed control in environmentally sensitive areas. Goats naturally consume diffuse knapweed and Canada thistle, and although the program was less effective than expected, goats will still be considered in future weed control projects. In 2010, goats were used to keep weeds under control at the Boulder Reservoir.
The city's Open Space and Mountain Parks department manages approximately of protected forest land west of the city, in accordance with a 1999 Forest Ecosystem Management Plan. The plan aims to maintain or enhance native plant and animal species, their communities, the ecological processes that sustain them and to reduce the wildfire risk to forest and human communities.
Climate
thumb|left|Autumn in Boulder
thumb|left|Snowfall is common in Boulder throughout the winter.
Boulder has a temperate climate typical for much of the state and receives many sunny or mostly sunny days each year. Boulder is considered semi-arid (Köppen: BSk) or humid subtropical (Köppen: Cfa) within the Köppen climate classification due to its relatively high yearly precipitation and average temperatures remaining above year-round.
Winter conditions range from generally mild to the occasional bitterly cold. Highs average in the mid to upper 40s °F (7–9 °C). There are 4.6 nights annually where the temperature drops to . Because of orographic lift, the mountains to the west often dry out the air passing over the Front Range, shielding the city from precipitation in winter, though heavy snowfalls may occur. Snowfall averages per season. Snow depth is usually shallow. Due to the high elevation, a strong warming sun can quickly melt snow cover during the day and Chinook winds bring rapid warm-ups throughout the winter months. The record low was on January 17, 1930. The coldest high temperature, , was on February 4, 1989. The warmest overnight low was on July 20, 1998, with a temperature of
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Demographics
thumb|A map of racial distribution in Boulder, 2020 US census. Each dot is one person:
Boulder is the principal city of the Boulder, CO Metropolitan Statistical Area.