**Boulder** is a city in the state of Colorado, in the United States. It is the county seat of Boulder County. Boulder is in the foothills of the Rocky Mountains. The city's height is 5,430 feet (1,660 m). It is 25 miles (40 km) northwest of Denver. In 2020, there were 108,250 people living the City of Boulder. The Boulder Metropolitan Statistical Area has 330,758 people living in it.

Boulder is famous for its history and its Western traditions. In the late 1960s, lots of hippies moved to Boulder. The main campus of the University of Colorado, the University of Colorado at Boulder, is also here. CU Boulder is the biggest university in Colorado. The city is thought to be one of the best cities for health, well-being, quality of life, education, and art.

History
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Panorama print of Boulder, 1900
On November 7, 1861, the government decided to build a university in Boulder. The legislature decided that the university would be run by the state. The first building was built in 1875. The cornerstone for the Old Main Building was laid on September 20, 1875. The university was officially opened on September 5, 1877.

In 1907, the city of Boulder passed an anti-saloon ordinance. This law said that saloons and bars could not do business in the city, and that people could not drink alcohol. In 1916, the entire state of Colorado started prohibition. In US History, the "Prohibition Era" was a time when all alcohol was illegal. People could not make, drink, buy, sell, or serve alcohol. Prohibition ended in 1933, when the Twenty-first Amendment to the United States Constitution was passed by Congress.

Demographics
------------

| Historical population |
| --- |
| Census | Pop. |  | %± |
| **1870** | 343 |  | — |
| **1880** | 3,069 |  | 794.8% |
| **1890** | 3,330 |  | 8.5% |
| **1900** | 6,150 |  | 84.7% |
| **1910** | 9,539 |  | 55.1% |
| **1920** | 11,066 |  | 16.0% |
| **1930** | 11,223 |  | 1.4% |
| **1940** | 12,958 |  | 15.5% |
| **1950** | 19,999 |  | 54.3% |
| **1960** | 37,718 |  | 88.6% |
| **1970** | 66,870 |  | 77.3% |
| **1980** | 76,685 |  | 14.7% |
| **1990** | 83,312 |  | 8.6% |
| **2000** | 94,673 |  | 13.6% |
| **2010** | 97,385 |  | 2.9% |
| **2020** | 108,250 |  | 11.2% |
| source: |

The 2020 United States Census said there are 108,250 people living in the City of Boulder. These people make up 43,565 households. The population density was 4,111.7 people per square mile (1,587.5 people/km²). According to the census, the people living in Boulder are 78.8% White, 1.3% black or African-American, 0.6% Native American, 6.4% Asian, 0.1% Pacific Islander, 4.7% of another race, and 8.1% of two or more races. 10.6% of the population are Hispanic or Latino of any race.

Geography
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Boulder's famous rock formations, the Flatirons.
Boulder is in Boulder Valley. This is a place where the Rocky Mountain meet the Great Plains. To the West of the city are some rock formations called the Flatirons. These are large flat pieces of stone that are tilted up on the foothills. The Flatirons are famous as a symbol of Boulder.

Boulder Creek flows through the City. Boulder Creek was named a long time before the city was built. It was named after the big granite boulders that have fallen into the creek over the years. Historians think that Boulder was named after Boulder Creek. The water in Boulder Creek comes from melting mountain snow and small rivers West of the city. Boulder Creek is a tributary of the South Platte River.

Boulder covers 27.4 square miles (71 km2) according to the U.S. Census Bureau. This includes 26.3 square miles (68 km2) of land and 1.0 square mile (3 km2) (3.8%) of water.

The 40th parallel (40 degrees north latitude) runs through Boulder. Baseline Road runs along the parallel today.

Flagstaff Mountain overlooks Boulder. The city is a few miles east of the Continental Divide and about 25 miles (40 km) northwest of Denver. Denver International Airport is about 50 miles (80 km) southeast of Boulder. The city gets its water from Arapahoe Glacier and Boulder Creek.

### Climate

Autumn in Boulder brings many sunny days
Snowfall is common in Boulder throughout the winter
Boulder has a dry climate. It has many sunny or mostly sunny days every year. According to the Köppen climate classification, the city's climate is "semi-arid" (Köppen *BSk*). Winters are cool, but sometimes can get very cold. During the winter, the high temperature is usually in the mid- to upper- 40s°F (7–9 °C). The low temperature in winter can be below −10 °F (−23 °C) on a few nights. Usually it does not stay below 0 °F (−18 °C) for many days at a time. 

Even though it is cold in the winter, Boulder does not get as much snow as the mountains. This is because of something called orographic lift. This means that the mountains in the west dry out the air as it passes over the Front Range. By the time the air gets to Boulder, most of the water and snow has been removed. Sometimes there are heavy snow storms, but not too often. The average amount of snow in Boulder is 85 inches (220 cm) per season, total. Usually only a few inches fall at a time. Because Boulder is so high up, the sun is very strong and hot, so the snow melts quickly. Sometimes Chinook Winds will make the temperature go up quickly and have the snow melt even faster.

Summer in Boulder is hot and dry. Usually there are 27 days during the summer that reach 90 °F (32 °C) or above. It is much cooler at night because of how high up the city is. The hottest temperature ever was on June 23, 1954 and July 11, 1954. On those days it was 104 °F (40 °C). The coldest temperature was in February 1989 and December 1990, when it was −24 °F (−31 °C).


| Climate data for Boulder, Colorado |
| --- |
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Record high °F (°C) | 73(23) | 79(26) | 80(27) | 88(31) | 95(35) | 104(40) | 104(40) | 101(38) | 100(38) | 90(32) | 79(26) | 76(24) | 104(40) |
| Average high °F (°C) | 45.7(7.6) | 49.1(9.5) | 55.8(13.2) | 62.7(17.1) | 71.7(22.1) | 82.2(27.9) | 87.2(30.7) | 85.0(29.4) | 77.4(25.2) | 66.7(19.3) | 52.6(11.4) | 46.1(7.8) | 65.2(18.4) |
| Average low °F (°C) | 19.2(−7.1) | 22.5(−5.3) | 27.7(−2.4) | 33.9(1.1) | 42.0(5.6) | 50.5(10.3) | 55.9(13.3) | 55.0(12.8) | 46.8(8.2) | 37.1(2.8) | 26.8(−2.9) | 20.6(−6.3) | 36.5(2.5) |
| Record low °F (°C) | −22(−30) | −24(−31) | −6(−21) | −3(−19) | 22(−5.6) | 30(−1.1) | 42(6) | 40(4) | 15(−9.4) | 5(−15) | −8(−22) | −24(−31) | −24(−31) |
| Average precipitation inches (mm) | .70(18) | .75(19) | 1.78(45) | 2.88(73) | 3.05(77) | 1.99(51) | 1.88(48) | 1.63(41) | 1.79(45) | 1.28(33) | 1.42(36) | .78(20) | 19.93(506) |
| Average snowfall inches (cm) | 11.5(29) | 10.1(26) | 15.3(39) | 12.6(32) | 1.1(2.8) | trace | 0(0) | 0(0) | 2.0(5.1) | 4.6(12) | 16.1(41) | 11.4(29) | 84.7(215) |
| Average precipitation days (≥ 0.01 in) | 4.7 | 5.7 | 7.5 | 9.5 | 12.1 | 9.5 | 11.5 | 10.3 | 8.2 | 6.4 | 5.5 | 5.6 | 96.5 |
| Average snowy days (≥ 0.1 in) | 4.6 | 5.3 | 5.8 | 3.9 | .3 | 0 | 0 | 0 | .6 | 1.5 | 4.7 | 5.0 | 31.7 |
| Source 1: NOAA (normals, 1971–2000) |
| Source 2: Weather.com (extremes) |

Politics and government
-----------------------

Boulder is a Home Rule Municipality. In Colorado, this means that Boulder's government was formed according to three different legal documents. These documents are: Article XX of the Constitution of the State of Colorado; Title 31, Article 1, Section 202 of the Colorado Revised Statutes; and Boulder's own Home Rule Charter. 

Boulder is very liberal and very Democratic. As of April 2012[update], registered voters in Boulder County were 41% Democrat, 20% Republican, 1% other parties, and 38% unaffiliated (not any specific party.) Boulder County includes the conservative suburbs of Boulder. Boulder is sometimes called the "People's Republic of Boulder" or "25 square miles surrounded by reality." This is a lot like nicknames given to other liberal cities that have more conservative areas surrounding them, like Columbia, Missouri; Madison, Wisconsin; and Austin, Texas.

Boulder was the first city in Colorado to pass a law that made it illegal to discriminate against people because of their sexual orientation. This law was passed by the Boulder City Council in 1974. The law was repealed (cancelled) by the voters that same year. In 1975, Boulder became the second city to ever grant a same-sex marriage license. The license was given by Boulder County Clerk Clela Rorex. Soon after a law was passed that said that marriage licenses could not be given to people of the same gender. In 1987, the people of Boulder voted again to make it illegal to discriminate against people because of their sexual orientation. This was passed by popular vote. Boulder became the first city in the United States that had this kind of a law that was passed by a direct vote of the people.

Sister cities
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Boulder has seven official sister cities:

* Tajikistan Dushanbe, Tajikistan (May 8, 1987)
* Nicaragua Jalapa, Nicaragua
* China Lhasa, Tibet, China (1987)
* Mexico Ciudad Mante, Mexico
* Japan Yamagata, Japan (1994)
* Cuba Yateras, Cuba
* Kenya Kisumu, Kenya

There are several landmarks in Boulder in honor of the sister cities. The Sister City Plaza was dedicated in May 17, 2007. It is on the east lawn of Boulder's Municipal Building. The plaza was built in honor of Boulder's relationships with its sister cities.

Sources
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1. 1 2 3 4  "Active Colorado Municipalities". Colorado Department of Local Affairs. Retrieved October 15, 2021.
2. 1 2 3  U.S. Geological Survey Geographic Names Information System: Boulder, Colorado
3. ↑  "Colorado Municipal Incorporations". State of Colorado, Department of Personnel & Administration, Colorado State Archives. December 1, 2004. Retrieved September 2, 2007.
4. ↑  "Shay Castle". *twitter.com*. Retrieved 16 November 2021.
5. ↑  "Boulder Mayor Pro Tem Junie Joseph appointed to National League of Cities committee". April 5, 2021. Retrieved 18 September 2021.
6. 1 2  "Decennial Census P.L. 94-171 Redistricting Data". United States Census Bureau, United States Department of Commerce. August 12, 2021. Retrieved September 7, 2021.
7. ↑  "ZIP Code Lookup". United States Postal Service. Retrieved October 20, 2014.
8. ↑  "Find a County". National Association of Counties. Retrieved 2008-01-31.
9. 1 2  "DP1: PROFILE OF GENERAL POPULATION AND HOUSING CHARACTERISTICS". United States Census Bureau. Retrieved September 13, 2023.
10. ↑  "2020 Population and Housing State Data". United States Census Bureau, Population Division. May 18, 2023. Archived from the original on June 29, 2022. Retrieved May 18, 2023.
11. ↑  "Best of Boulder". City of Boulder. Retrieved 2011-02-11.
12. ↑  "C.U. History". BoulderGuide. June 30, 2009. Archived from the original on 2011-07-21. Retrieved 2010-12-09.
13. ↑  "A Boulder Timeline". Boulder History Museum. Archived from the original on 2013-03-13. Retrieved 2010-01-17.
14. ↑  "Brief History of Colorado". Archived from the original on March 7, 2008.
15. ↑  Moffatt, Riley. *Population History of Western U.S. Cities & Towns, 1850–1990*. Lanham: Scarecrow, 1996, 67.
16. ↑  "Contact." Sirna Therapeutics. December 8, 2004. Retrieved March 3, 2012. "2950 Wilderness Place Boulder, CO 80301"
17. ↑  "Boulder Area Sustainability Information Network". Boulder Community Network. August 27, 1999. Retrieved 2010-12-09.
18. ↑  D. B. Crawley (2007). "Creating weather files for climate change and urbanization impacts analysis" (PDF). *Proceedings of Building Simulation*: 1075–1082. Archived from the original (PDF) on 2011-09-20. Retrieved 2012-11-11.
19. ↑  "Climatography of the United States No. 20 1971–2000: BOULDER AP, CO" (PDF). National Oceanic and Atmospheric Administration. July 2011. Archived from the original (PDF) on 2012-10-18.
20. ↑  "Monthly Averages for Boulder, CO". The Weather Channel. Archived from the original on 2012-10-23.
21. ↑  "Voter Registration Statistics". Boulder County. Archived from the original on 2012-07-21. Retrieved 2012-04-14.
22. ↑  Herel, Suzanne (February 14, 2004). "San Francisco not the first to marry couples of the same gender". *San Francisco Chronicle*. Archived from the original on 2012-04-18. Retrieved 2010-12-09.
23. ↑  "Boulder Sister City Program". *City of Boulder, Colorado*. Retrieved September 9, 2011.
24. ↑  The Boulder Sister City Plaza