[32] In May 1859, Denver City residents donated 53 lots to the Leavenworth & Pike's Peak Express in order to secure the region's first overland wagon route.

Offering daily service for "passengers, mail, freight, and gold", the Express reached Denver on a trail that trimmed westward travel time from twelve days to six.

This disagreement on the validity of Treaty of Fort Wise escalated to bring about the Colorado War of 1864 and 1865, during which the brutal Sand Creek massacre against Cheyenne and Arapaho peoples occurred.

The aftermath of the war was the dissolution of the reservation in Eastern Colorado, the signing of Medicine Lodge Treaty which stipulated that the Cheyenne and Arapaho peoples would be relocated outside of their traditional territory.

Soon, in addition to the elite and a large middle class, Denver had a growing population of immigrant German, Italian, and Chinese laborers, soon followed by African Americans from the Deep South and Hispanic workers.

Unlike the earlier organization that was active in the rural South, KKK chapters developed in urban areas of the Midwest and West, including Denver, and into Idaho and Oregon.

A major fire at the facility in 1957, as well as leakage from nuclear waste stored at the site between 1958 and 1968, resulted in the contamination of some parts of Denver, to varying degrees, with plutonium-239, a harmful radioactive substance with a half-life of 24,200 years.

[52] A 1981 study by the Jefferson County health director, Carl Johnson, linked the contamination to an increase in birth defects and cancer incidence in central Denver and nearer Rocky Flats.

[63] On August 10–15, 1993, Denver hosted the Catholic Church's 6th World Youth Day, which was attended by an estimated 500,000, making it the largest gathering in Colorado history.

Based on 30-year averages obtained from NOAA's National Climatic Data Center for the months of December, January and February, Weather Channel ranked Denver the 18th-coldest major U.S. city as of 2014[update].

Throughout that time, the company held a large employee base in the Denver area, which is home to the United Airlines Flight Training Center in the Central Park neighborhood.

[117] Denver's west-central geographic location in the Mountain Time Zone (UTC−7) also benefits the telecommunications industry by allowing communication with both North American coasts, South America, Europe, and Asia on the same business day.

Denver's location on the 105th meridian at over one mile (1.6 km) in elevation also enables it to be the largest city in the U.S. to offer a "one-bounce" real-time satellite uplink to six continents in the same business day.

[119] The Downtown region has seen increased real estate investment[120][needs update] with the construction of several new skyscrapers from 2010 onward and major development around Denver Union Station.

Qdoba Mexican Grill, Noodles & Company, and Good Times Burgers & Frozen Custard originated in Denver, but have moved their headquarters to the suburbs of Wheat Ridge, Broomfield, and Golden, respectively.

More recent Denver-based artists include India Arie, Nathaniel Rateliff & the Night Sweats, The Lumineers, Air Dubai, The Fray, Flobots, Cephalic Carnage, Axe Murder Boyz, Deuce Mob, Havok, Bloodstrike, Primitive Man, and Five Iron Frenzy.

The Denver Broncos of the National Football League have drawn crowds of over 70,000 since their origins in the early 1960s, and continue to draw fans today to their current home Empower Field at Mile High.

The Major League Soccer team Colorado Rapids play in Dick's Sporting Goods Park, an 18,000-seat soccer-specific stadium opened for the 2007 MLS season in the Denver suburb of Commerce City.

In 2020, during the George Floyd protests, because of Stapleton's demonstrated racism and prominent membership in the Ku Klux Klan, neighborhood residents changed the name to Central Park.

The boxer-turned-activist Rodolfo "Corky" Gonzales formed an organization called the Crusade for Justice, which battled police brutality, fought for bilingual education, and, most notably, hosted the First National Chicano Youth Liberation Conference in March 1969.

The 1972 Convention was notable for nominating Tonie Nathan for vice president, the first woman, as well as the first Jew, to receive an electoral vote in a United States presidential election.

East of Colorado Boulevard, the naming convention of streets takes on a predictable pattern of going through the alphabet by using each letter twice (i.e. AA, BB, CC, DD, through YY – there is no Z).

This is due in large part to Front Range cities like Boulder, Fort Collins and Denver placing an emphasis on legislation, programs and infrastructure developments that promote cycling as a mode of transportation.

In June, the city ordered the companies to remove them[195] and acted quickly to create an official program, including a requirement that scooters be left at RTD stops and out of the public right-of-way.

Additionally, RTD operates ten rail lines, the A, B, D, E, G, H, L, N, R, and W, with a total of 113 miles (182 km) of track, serving 77 stations, 35 of which are located within the City of Denver proper.

A commuter rail connection to Boulder and its suburb of Longmont, also part of the FasTracks ballot initiative and an extension of the B Line, is planned to be finished by RTD, but no construction funds have yet been identified prior to 2040.

[211] Greyhound Lines, the intercity bus operator, has a major hub in Denver, with routes to New York City, Portland, Reno, Las Vegas, and their headquarters, Dallas.

[212] Front Range Passenger Rail is a current proposal (as of 2023) to link the cities from Pueblo in the south, north to Fort Collins and possibly to Cheyenne, Wyoming.

Further development of a mountain corridor rail option, though publicly popular, has been met with resistance from politicians, namely the director of Colorado Department of Transportation.

Trains stop in Denver at historic Union Station, where travelers can access RTD's 16th Street Free MallRide or use light rail to tour the city.