# Timeline of Colorado history

This timeline is a chronology of significant events in the history of the U.S. State of Colorado and the historical area now occupied by the state.

## Timeline
### 2020s

| Year | Date | Event |
| 2025 | March 13 | American Airlines Flight 1006 catches fire on the tramac after making an emergency landing at Denver International Airport. At least a dozen people are sent to area hospitals with minor injuries. |
| 2024 | December 14 | Travis Hunter of the University of Colorado Buffaloes football team wins the 2024 Heisman Trophy. |
| 2024 | November 5 | In the 2024 General Election, Colorado voters elect ten U.S. Presidential Electors for Vice President Kamala Harris. Voters elect four Republicans to the U.S. House of Representatives: Jeff Hurd for the 3rd District, Lauren Boebert for the 4th District, Jeff Crank for the 5th District, and Gabe Evans for the 8th District; and re-elect four incumbent Democratic U.S. Representatives. Democrats retain control of the Colorado General Assembly. Voters add Reproductive Freedom Amendment 79 to the Constitution of Colorado. |
| 2024 | September 12 | The United States Army decommissions the Pueblo Chemical Depot. |
| 2024 | August 12 | A Mesa County jury finds former Mesa County Clerk Tina Peters guilty of one count of conspiracy to commit criminal impersonation, three counts of attempting to influence a public servant, first-degree official misconduct, violation of duty, and failure to comply with an order from the Secretary of State in her attempt to prove election fraud in the 2020 U.S. presidential election. The jury finds Peters not guilty of a second count of conspiracy to commit criminal impersonation, criminal impersonation, and identity theft. Peters is the first election official convicted of criminal charges involving stolen election conspiracy theories of the 2020 election. |
| 2024 | August 11 | Jennifer Valente of Colorado Springs wins her second consequetive gold medal for the women's cycling omnium with 144 points at the Games of the XXXIII Olympiad in Paris. She becomes the most decorated U.S. female Olympic cyclist ever with three gold and two silver Olympic medals. |
| 2024 | August 10 | Mallory Swanson of Highlands Ranch scores the lone goal as Team USA defeats Brazil 1–0 to win the women's football (soccer) tournament at the Games of the XXXIII Olympiad in Paris. Mallory with four goals in tournament play, Sophia Smith of Windsor with three goals and two assists, and Team Captain Lindsey Horan of Golden with two assists receive Olympic gold medals. |
| 2024 | August 7 | Sarah Hildebrandt of Colorado Springs wins the gold medal for women's 50 kilogram freestyle wrestling at the Games of the XXXIII Olympiad in Paris. |
| 2024 | August 7 | Team USA wins the women's cycling team pursuit with an average speed of 36.625 mph (58.942 km/h) at the Games of the XXXIII Olympiad in Paris. As a member of the four rider team, Jennifer Valente of Colorado Springs wins an Olympic gold medal. |
| 2024 | August 5 | Valarie Allman of Longmont wins her second consequetive gold medal for the women's discus throw with a throw of 195.2 feet (59.50 m) at the Games of the XXXIII Olympiad in Paris. |
| 2024 | June 27 | Nathan MacKinnon of the Colorado Avalanche wins both the NHL Hart Memorial Trophy and the Ted Lindsay Award. |
| 2024 | June 25 | Greg Lopez wins the congressional vacancy election for Colorado's 4th congressional district seat vacated by Ken Buck on March 22. Lopez will take office on July 8. |
| 2024 | May 8 | Nikola Jokić (Никола Јокић) of the Denver Nuggets wins his third NBA MVP Award in four seasons. |
| 2024 | April 13 | The University of Denver men's ice hockey team defeats the Boston College men's ice hockey team by 2–0 to win the NCAA Division I men's ice hockey championship for a record tenth time. |
| 2024 | March 22 | Ken Buck resigns as U.S. Representative for Colorado's 4th congressional district, reducing the Republican majority in the United States House of Representatives to 218–213. Buck cites congressional dysfunction as the reason for his resignation. |
| 2024 | March 4 | The United States Supreme Court rules in an unsigned ruling with no dissent in Trump v. Anderson that the Colorado Supreme Court erred when it blocked Donald Trump from seeking public office. |
| 2024 | February 8 | The Town of Keystone incorporates as a home rule municipality. |
| 2024 | January 23 | Former Colorado Rockies third baseman Todd Helton is elected to the Baseball Hall of Fame. |
| 2023 | December 27 | U.S. Representative Lauren Boebert announces that she will not run for re-election from Colorado's 3rd congressional district in southwestern Colorado, but that she will instead seek election from Colorado's 4th congressional district in northeastern Colorado. |
| 2023 | December 19 | In a four-to-three decision, the Colorado Supreme Court overrules District Court Judge Sarah B. Wallace and rules that Donald Trump is no longer eligible to seek public office under the 14th Amendment to the United States Constitution. |
| 2023 | November 17 | Colorado District Court Judge Sarah B. Wallace rules that Donald Trump did incite an insurrection against the United States in the January 6 United States Capitol attack, but the 14th Amendment to the United States Constitution does not preclude his appearance on a Colorado Presidential Primary ballot. |
| 2023 | October 3 | U.S. Representative Ken Buck votes with seven other Republican representatives to remove Kevin McCarthy as Speaker of the United States House of Representatives. |
| 2023 | September 17 | Sepp Kuss, "The Durango Kid," of Durango wins the 2023 Vuelta a España with Team Jumbo–Visma. |
| 2023 | September 15 | The United States Board on Geographic Names votes to rename 14,271-foot (4,350 m) Mount Evans as Mount Blue Sky. |
| 2023 | September 13 | Five Colorado restaurants are awarded Michelin Guide Stars: Bosq in Aspen; Frasca Food and Wine in Boulder, and Beckon, Brutø, and The Wolf's Tailor in Denver. |
| 2023 | July 22 | Sophia Smith of Windsor scores two goals in her first FIFA Women's World Cup appearance and team co-captain Lindsey Horan of Golden scores another goal to lead the United States to a 3–0 victory over Vietnam in Auckland, New Zealand. |
| 2023 | July 17 | Mike Johnston is inaugurated as the 46th Mayor of the City and County of Denver. |
| 2023 | June 23 | Trey Parker and Matt Stone reopen Casa Bonita in Lakewood which they modestly bill as The Greatest Restaurant in the World! |
| 2023 | June 13 | Ten people are wounded in a Denver gunfight in the hours after the Denver Nuggets won the 2023 NBA Finals. |
| 2023 | June 12 | The Denver Nuggets defeat the Miami Heat four games to one to win the 2023 NBA Finals and the Larry O'Brien Championship Trophy, their first in franchise history. Nikola Jokić (Никола Јокић) wins the Bill Russell NBA Finals MVP Award. |
| 2023 | May 3 | A Denver man is shot to death in an altercation with another Tesla driver over access to an electric charging station in Edgewater. |
| 2023 | March 11 | Mikaela Shiffrin of Eagle-Vail wins the slalom ski race at Åre, Sweden setting the all-time world record with 87 International Ski Federation World Cup wins. |
| 2022 | December 31 | The U.S. National Institute of Standards and Technology eliminates the official use of the U.S. survey foot, changing the official U.S. definition of the foot from approximately 304.800 609 601 219 mm to the international foot of exactly 304.8 mm. This slight measurement change alters many traditional survey and elevation measures in Colorado. The Mile-High City is now officially 0.127 inches (3.219 mm) lower than before. |
| 2022 | November 19 | A gunman invades the Club Q nightclub in Colorado Springs and shoots 24 people, killing five, and causes injuries to six more before being subdued by club patrons. The gunman is later arranged on 305 counts. |
| 2022 | November 8 | Colorado voters reelect Governor Jared Polis and the other four incumbent state officers. Brittany Pettersen is elected U.S. Representative for the 7th Congressional District, and Yadira Caraveo is elected for the new 8th Congressional District. U.S. Senator Michael Bennet and the six incumbent U.S. Representatives are reelected. Democrats retain control of the Colorado General Assembly. |
| 2022 | October 12 | U.S. President Joe Biden issues a proclamation creating Camp Hale-Continental Divide National Monument on 53,804 acres (217.74 km$^2$) of White River National Forest. The United States Forest Service will manage the monument. |
| 2022 | June 26 | The Colorado Avalanche defeat the world champion Tampa Bay Lightning four games to two to win their third Stanley Cup. Cale Makar is awarded the Conn Smythe Trophy. |
| 2022 | June 21 | Cale Makar of the Colorado Avalanche wins the James Norris Memorial Trophy. |
| 2022 | June 8 | The Walton-Penner family agrees to purchase the Denver Broncos Football Club for $4.65 billion USD, a new world record price for a professional sports franchise. |
| 2022 | May 11 | Nikola Jokić (Никола Јокић) of the Denver Nuggets wins his second consecutive NBA MVP Award. |
| 2022 | April 4 | Colorado Governor Jared Polis signs the Reproductive Health Equity Act which guarantees access to reproductive care and affirms the rights of pregnant people to continue or terminate a pregnancy. |
| 2021 | December 30 | Fanned by winds gusting over 110 miles per hour (180 km/h), the Marshall Fire burns 6,026 acres (24.39 km$^2$) in southeastern Boulder County in six hours and forces the evacuation of more than 30,000 residents. The wildfire kills two people and destroys 1,084 homes and seven businesses and damages another 149 homes and 40 businesses with total losses estimated to exceed US$2 billion, making it the most expensive natural disaster in state history. |
| 2021 | December 27 | A Denver gunman kills three Denver residents and two Lakewood residents before being killed by seriously wounded Lakewood Police Agent Ashley Ferris. |
| 2021 | December 10 | A mere 0.3 inch (0.8 cm) of snow falls on Denver, the latest first seasonal snowfall in recorded Denver history. |
| 2021 | November 16 | The Kruger Rock Fire ignites near Estes Park. A fire retardant tanker plane crashes while battling the wildfire, killing its pilot. |
| 2021 | October 20 | The United States Forest Service and Colorado Parks and Wildlife announce a first-of-its-kind agreement to create Sweetwater Lake State Park, Colorado's 43rd state park. |
| 2021 | September 17 | Meow Wolf Convergence Station opens in Denver. |
| 2021 | August 2 | Valarie Allman of Longmont wins the gold medal for the women's discus throw at the Games of the XXXII Olympiad in Tokyo. |
| 2021 | July 26 | The United States Space Force recommissions Peterson Air Force Base, Schriever Air Force Base, and Cheyenne Mountain Air Force Station as Peterson Space Force Base, Schriever Space Force Base, and Cheyenne Mountain Space Force Station. |
| 2021 | June 27 | The first of a series of summer mudslides precipitated by the 2020 Grizzly Creek Fire closes Interstate 70 through Glenwood Canyon. |
| 2021 | June 8 | Nikola Jokić (Никола Јокић) of the Denver Nuggets wins the NBA MVP Award. |
| 2021 | June 4 | The United States Space Force recommissions Buckley Air Force Base as Buckley Space Force Base. |
| 2021 | May 9 | A Colorado Springs man shoots six people to death at a family birthday party before taking his own life. |
| 2021 | March 30 | A Trimble woman is killed by a black bear with two yearling cubs on a trail near her home. |
| 2021 | March 22 | An Arvada man shoots ten people to death at a grocery store in Boulder. |
| 2021 | March 14 | A blizzard dumps up to three feet (90 cm) of snow on the Front Range Urban Corridor. |
| 2020 | December 10 | Elizabeth Ann, a female black-footed ferret, is born at the National Black-footed Ferret Conservation Center in Wellington. Elizabeth Ann becomes the first U.S. endangered species to be successfully cloned. |
| 2020 | December 3 | TIME names 15-year-old Gitanjali Rao of Lone Tree its first ever "Kid of the Year". |
| 2020 | November 3 | In the 2020 General Election, Colorado voters elect nine U.S. Presidential Electors for Joe Biden, elect John Hickenlooper as a new U.S. Senator, elect Lauren Boebert as the new 3rd District U.S. Representative, and re-elect the other six incumbent U.S. Representatives. Democrats retain control of the Colorado General Assembly. |
| 2020 | October 30 | Fishers Peak State Park opens to the public. |
| 2020 | October 17 | The Calwood Fire ignites 3 miles (5 km) northwest of Jamestown. As many as 495 firefighters battle the wildfire as it consumes 10,106 acres (41 km$^2$) of forest and 26 homes. |
| 2020 | October 14 | The East Troublesome Fire ignites north of Parshall. As many as 794 firefighters battle the wildfire as it consumes 193,812 acres (784 km$^2$) of forest and rangeland to become the second most extensive Colorado wildfire in recorded history. Thousands evacuated, more than 300 homes destroyed, and two residents killed. The wildfire would become the most expensive in Colorado history with insured losses alone of $543 million. |
| 2020 | September 17 | The Mullen Fire ignites 7 miles (11 km) west of Centennial, Wyoming. As many as 1,254 firefighters battle the wildfire as it spreads through Carbon County, Wyoming, Albany County, Wyoming, and Jackson County, Colorado and consumes 176,878 acres (716 km$^2$) of forest. |
| 2020 | September 6 | Lightning ignites the Middle Fork Fire 10 miles (16 km) north of Steamboat Springs. As many as 136 firefighters battle the wildfire as it consumes 20,517 acres (83 km$^2$) of forest. |
| 2020 | August 14 | Humans ignite the Williams Fork Fire 9.5 miles (15.3 km) southwest of Fraser. As many as 396 firefighters battle the wildfire as it consumes 14,833 acres (60 km$^2$) of forest. |
| 2020 | August 13 | The Cameron Peak Fire ignites 15 miles (24 km) southwest of Red Feather Lakes. As many as 1,903 firefighters battle the wildfire as it consumes 208,913 acres (845 km$^2$) of forest to become the most extensive Colorado wildfire in recorded history, surpassing the ongoing Pine Gulch Fire. Thousands evacuated, 209 homes destroyed. |
| 2020 | August 10 | Humans ignite the Grizzly Creek Fire in Glenwood Canyon of the Colorado River. The wildfire closes Interstate 70, the Union Pacific Railroad, and the Amtrak California Zephyr for two weeks. As many as 889 firefighters battle the wildfire as it consumes 32,631 acres (132 km$^2$) of forest. |
| 2020 | July 31 | Lightning ignites the Pine Gulch Fire 18 miles (29 km) north of Grand Junction. As many as 466 firefighters battle the wildfire as it consumes 139,007 acres (563 km$^2$) of forest and rangeland to become the most extensive Colorado wildfire in recorded history, only to be surpassed by the Cameron Peak Fire seven weeks later. |
| 2020 | June 27 | Aurora Police in riot gear disperse thousands of protestors in the Violin Protest of the death of Elijah McClain. |
| 2020 | June 24 | Colorado Governor Jared Polis announces a state investigation into the unprovoked death of Elijah McClain while in the custody of Aurora Police. |
| 2020 | June 16 | Colorado Governor Jared Polis issues a statewide COVID-19 mask order. |
| 2020 | April 26 | Colorado Governor Jared Polis rescinds his statewide Stay-at-Home order while requiring continued COVID-19 precautions. |
| 2020 | April 1 | The 2020 United States census enumerates the population of the State of Colorado, later determined to be 5,773,714, an increase of 14.80% since the 2010 United States census. Colorado becomes the 21st most populous of the 50 U.S. states and will gain an 8th Congressional District. |
| 2020 | March 28 | U.S. President Donald Trump declares that a major disaster exists in the State of Colorado as a result of the COVID-19 pandemic. |
| 2020 | March 25 | Colorado Governor Jared Polis issues the first Colorado Stay-at-Home order effective at 6:00 a.m. the following morning. |
| 2020 | March 13 | A woman in El Paso County becomes the first person in Colorado to die from the COVID-19 virus. |
| 2020 | March 10 | Colorado Governor Jared Polis declares a Colorado state of emergency in response to the COVID-19 pandemic. |
| 2020 | March 5 | A visitor to Summit County becomes the first person in Colorado to test positive for the COVID-19 virus. |
| 2020 | February 11 | United States Senator Michael Bennet of Denver ends his campaign for President of the United States. |
| 2020 | February 4 | A Fort Collins trail runner is attacked by a young mountain lion, but is able to strangle the animal. |

### 2010s

| Year | Date | Event |
| 2019 | October 25 | Reprise Records releases the Neil Young album Colorado. |
| 2019 | September 8 | Lightning ignites the Decker Fire in the Sangre de Cristo Wilderness. Up to 720 firefighters will battle the wildfire which will consume 8,959 acres (36 km$^2$) of forest. |
| 2019 | August 30 | Elijah McClain of Aurora dies six days after an unprovoked detention by Aurora police. |
| 2019 | August 15 | Former governor John Hickenlooper ends his campaign for President of the United States. |
| 2019 | July 20 | An ambient air temperature of 115 °F (46.1 °C) at John Martin Dam sets the official Colorado all-time high temperature record. |
| 2019 | May 7 | Two armed students attack STEM School Highlands Ranch killing one student and wounding eight others. |
| 2019 | May 2 | United States Senator Michael Bennet of Denver announces his candidacy for President of the United States. |
| 2019 | April 26 | The Regional Transportation District begins operation of its commuter rail G line between Denver Union Station and Wheat Ridge. |
| 2019 | March 17 | Mikaela Shiffrin of Eagle-Vail wins her third consecutive International Ski Federation Women's Overall World Cup. |
| 2019 | March 13 | Winter Storm Ulmer undergoes explosive cyclogenesis as it rips across the Southern Rocky Mountains of Colorado. The bomb cyclone blizzard with hurricane-force winds sets all-time record low barometric pressure readings across the state. |
| 2019 | March 4 | Former governor John Hickenlooper of Denver announces his candidacy for President of the United States. |
| 2019 | January 8 | Jared Polis of Boulder assumes office as the forty-third Governor of the State of Colorado. |
| 2018 | November 6 | In the 2018 General Election, Democrats win all five Colorado statewide offices and control of the Colorado General Assembly. Republicans retain three of the state's seven Congressional seats. |
| 2018 | August 18 | The Denver Outlaws defeat the Dallas Rattlers 16 to 12 to win their third Major League Lacrosse Steinfeld Cup. |
| 2018 | June 28 | Lightning ignites the Weston Pass Fire 9 miles (14 km) southwest of Fairplay. The wildfire will burn 13,023 acres (53 km$^2$) of forest. |
| 2018 | June 7 | An illegal campfire ignites the Spring Creek Fire 9 miles (14 km) northeast of Fort Garland. The wildfire will burn 251 homes and 108,045 acres (437 km$^2$) of forest. |
| 2018 | June 1 | An antique steam locomotive ignites the 416 Fire 10 miles (16 km) north of Durango. The wildfire will burn 54,129 acres (219 km$^2$) of forest over a period of six months. |
| 2018 | April 17 | The Mile Marker 117 Fire ignites 17 miles (27 km) north of Pueblo. The wildfire will burn 42,795 acres (173 km$^2$) of grassland. |
| 2018 | April 17 | The Badger Hole Fire ignites near Walsh. The wildfire will burn 50,815 acres (206 km$^2$) of grassland with 33,609 acres (136 km$^2$) in Colorado and 17,206 acres (70 km$^2$) in Kansas. |
| 2018 | March 18 | Mikaela Shiffrin of Eagle-Vail wins her second consecutive International Ski Federation Women's Overall World Cup. |
| 2018 | March 17 | The attack submarine USS Colorado (SSN-788) is commissioned at the Naval Submarine Base New London. |
| 2018 | March 2 | The Colorado House of Representatives expels State Representative Steve Lebsock for inappropriate behavior. |
| 2018 | February 15 | Mikaela Shiffrin of Eagle-Vail wins the Women's Alpine Skiing Giant Slalom Gold Medal at the XXIII Olympic Winter Games in Pyeongchang, Korea. |
| 2018 | February 11 | Red Gerard of Silverthorne wins the Men's Snowboarding Slopestyle Gold Medal at the XXIII Olympic Games in Pyeongchang, Korea. |
| 2017 | November 19 | Martin Truex Jr. of Denver wins the 2017 NASCAR Cup. |
| 2017 | October 8 | Eleven-year-old Gitanjali Rao of Lone Tree wins the 2017 Discovery Education 3M Young Scientist Challenge for her invention of a device that can detect lead in water faster than existing techniques. |
| 2017 | April 10 | United States Circuit Court Judge Neil Gorsuch of Boulder is sworn in as the 101st Associate Justice of the Supreme Court of the United States. |
| 2017 | March 18 | Mikaela Shiffrin of Eagle-Vail wins the International Ski Federation Women's Overall World Cup. |
| 2016 | August 20 | The Denver Outlaws defeat the Ohio Machine 19 to 18 to win their second Major League Lacrosse Steinfeld Cup. |
| 2016 | June 19 | A child starts the Beaver Creek Fire near Walden. The wildfire will burn one home, 16 outbuildings, and 38,380 acres (155 km$^2$) of forest. |
| 2016 | March 22 | The Regional Transportation District begins operation of its commuter rail A line between Denver Union Station and Denver International Airport. |
| 2016 | February 7 | The Denver Broncos defeat the Carolina Panthers 24 to 10 to win Super Bowl 50. Von Miller is named the Super Bowl Most Valuable Player. Quarterback Peyton Manning wins his second Super Bowl and his 200th NFL game. |
| 2016 | January 24 | The Denver Broncos defeat the New England Patriots 20 to 18 to win the American Football Conference Championship for the eighth time. |
| 2015 | February 19 | U.S. President Barack Obama issues a proclamation creating Browns Canyon National Monument on 21,586 acres (87 km$^2$) of Bureau of Land Management land. |
| 2015 | January 2 | Cory Gardner of Yuma assumes office as the junior United States senator from Colorado. |
| 2014 | October 6 | Immediately following a declination by the United States Supreme Court, Colorado Attorney General John Suthers declares that same-sex marriage will be legal in Colorado as soon as legal stays can be lifted. |
| 2014 | August 23 | The Denver Outlaws defeat the Rochester Rattlers 12 to 11 to win their first Major League Lacrosse Steinfeld Cup. |
| 2014 | July 26 | The Regional Transportation District reopens Denver Union Station marking the conclusion of a $56 million redevelopment into a regional multimodal transit hub. |
| 2014 | May 25 | A 40,000,000 cu yd (31,000,000 m$^3$) landslide breaks loose on Grand Mesa near Collbran, hits speeds of more than 50 mph (80 km/h), and kills three men. |
| 2014 | February 21 | Mikaela Shiffrin of Vail wins the women's alpine skiing slalom gold medal at the XXII Olympic Winter Games in Sochi, Russia. |
| 2014 | February 2 | The Denver Broncos lose Super Bowl XLVIII to the Seattle Seahawks 43 to 8 to become the first team to lose the Super Bowl five times. |
| 2014 | January 19 | The Denver Broncos defeat the New England Patriots 26 to 16 to win the American Football Conference Championship for the seventh time. |
| 2014 | January 1 | Colorado becomes the first U.S. state to legalize cannabis for recreational use. |
| 2013 | September 12 | Floods along the Front Range Urban Corridor kill 9 people. More than 22,000 residents are evacuated including 1,000 by military helicopters. More than 30,000 homes are damaged and 1800 are destroyed. Total damages will exceed $2.9 billion. |
| 2013 | September 10 | A recall election removes State Senate President John Morse and State Senator Angela Giron from office. |
| 2013 | July 18 | The Royal Gorge wildfire destroys buildings and the aerial tram at the Royal Gorge Bridge and Park after starting on June 11. |
| 2013 | June 13 | The Black Forest fire north of Colorado Springs surpasses the Waldo Canyon fire as the most destructive in state history. A total of 486 homes will be destroyed by June 20. |
| 2013 | June 11 | Lightning ignites the Big Meadows fire in Rocky Mountain National Park. |
| 2013 | June 5 | Lightning ignites the first of the West Fork Complex fires near Wolf Creek Pass. The wildfires will burn 109,049 acres (441 km$^2$) of forest. |
| 2013 | May 1 | An Act of the Colorado General Assembly makes civil unions legal in Colorado for both conventional and same-sex couples, although same-sex marriage remains illegal for 17 months. |
| 2013 | March 20 | Governor John Hickenlooper signs three bills intended to curb firearm violence. |
| 2013 | March 19 | Tom Clements, executive director of the Colorado Department of Corrections, is assassinated at his home in Monument. |
| 2012 | December 10 | David J. Wineland of the National Institute of Standards and Technology and the University of Colorado Boulder and Serge Haroche receive the 2012 Nobel Prize in Physics. |
| 2012 | November 6 | Voters approve Colorado Amendment 64 legalizing possession of small quantities of cannabis. |
| 2012 | September 28 | The History Colorado Center opens in Denver. |
| 2012 | September 21 | U.S. President Barack Obama issues a proclamation creating Chimney Rock National Monument on 4,726 acres (19 km$^2$) of the San Juan National Forest. |
| 2012 | July 30 | Missy Franklin of Centennial wins the first of four gold medals in swimming at the Games of the XXX Olympiad in London. |
| 2012 | July 20 | A gunman opens fire in a cinema in an Aurora, Colorado screening The Dark Knight Rises, killing 12 people and wounding 70 others. |
| 2012 | June 25 | Sparks ignite the Last Chance Fire on the prairie near Last Chance. This wildfire will burn four homes, seven outbuildings, and 44,000 acres (178 km$^2$) of grassland in a few hours. |
| 2012 | June 23 | The Waldo Canyon Fire ignites west of Colorado Springs. The wildfire will destroy 347 homes. |
| 2012 | June 9 | A lightning strike ignites the High Park Fire west of Fort Collins. The wildfire will kill one person and destroy 248 homes and 87,250 acres (353 km$^2$) of forest. |
| 2012 | April 28 | The History Colorado Center opens in Denver. |
| 2012 | March 16 | Lindsey Vonn of Vail wins her fourth International Ski Federation Women's Overall World Cup. |
| 2011 | November 18 | The Clyfford Still Museum opens in Denver. |
| 2011 | October 22 | Missy Franklin of Centennial sets her first swimming world record at the Fédération Internationale de Natation (FINA) Swimming World Cup in Berlin. |
| 2011 | September 23 | Occupy Denver begins a protest of the growing disparity of wealth and political power in the United States. |
| 2011 | July 18 | Michael Hancock is inaugurated as the 45th Mayor of the City and County of Denver. |
| 2011 | April 1 | CenturyLink, Inc. completes its $24 billion acquisition of the larger Qwest Communications International, Inc. of Denver. |
| 2011 | January 12 | Deputy Major Bill Vidal assumes office as the 44th Mayor of the City and County of Denver replacing John Hickenlooper. |
| 2011 | January 11 | John Hickenlooper assumes office as the forty-second Governor of the State of Colorado. |
| 2010 | November 21 | The Colorado Rapids defeat FC Dallas 2 to 1 to win their first Major League Soccer Cup. |
| 2010 | November 6 | The City of Castle Pines North votes to shorten its name to the City of Castle Pines. The City of Castle Pines is the youngest of the 272 active municipalities of the State of Colorado. |
| 2010 | October 14 | Workers uncover a trove of Pleistocene fossils at the Snowmastodon site while excavating a reservoir near Snowmass Village. |
| 2010 | September 6 | The Fourmile Canyon fire begins west of Boulder. The wildfire will destroy 169 homes. |
| 2010 | April 1 | The 2010 United States census enumerates the population of the State of Colorado, later determined to be 5,029,196, an increase of 16.92% since the 2000 United States census. Colorado becomes the 22nd most populous of the 50 U.S. states. |
| 2010 | March 14 | Lindsey Vonn of Vail wins her third consecutive International Ski Federation Women's Overall World Cup. |
| 2010 | February 17 | Lindsey Vonn of Vail wins the women's alpine skiing downhill gold medal at the XXI Olympic Winter Games at Whistler Blackcomb. |

### 2000s

| Year | Date | Event |
| 2009 | October 15 | The balloon boy hoax discombobulates emergency services in northeastern Colorado. |
| 2009 | August 7 | A Ouray woman is killed by a black bear at her home. |
| 2009 | March 15 | Lindsey Vonn of Vail wins her second consecutive International Ski Federation Women's Overall World Cup. |
| 2009 | February 27 | The Rocky Mountain News, the region's oldest and second highest circulation newspaper, publishes its last edition just 55 days before of its sesquicentennial (c.f. April 23, 1859.) The Denver Post survives as the city's only major newspaper. |
| 2009 | January 21 | Michael Bennet of Denver assumes office as the junior United States senator from Colorado. |
| 2009 | January 3 | Mark Udall of Eldorado Springs assumes office as the junior United States senator from Colorado. |
| 2008 | August 28 | Barack Obama accepts the nomination of the Democratic National Convention in Denver for President of the United States. |
| 2008 | August 13 | Jack Weil, founder and CEO of Rockmount Ranch Wear, dies at his home in Denver at age 107. |
| 2008 | August 4 | The extension of Interstate Highway I-270 from I-76 to the intersection of I-25 and US 36 opens to traffic, lengthening I-270 to 7.107 miles (11.438 km). |
| 2008 | June 10 | Lightning ignites the Bridger Fire on the U.S. Army Piñon Canyon Maneuver Site. The fire will burn 46,612 acres (189 km$^2$) of forest and grassland. |
| 2008 | March 15 | Lindsey Vonn of Vail wins the International Ski Federation 2008 Women's Overall World Cup. |
| 2008 | February 16 | The Bradford Washburn American Mountaineering Museum opens in Golden. |
| 2008 | February 11 | The Luis A. Jiménez, Jr. sculpture Blue Mustang is unveiled at Denver International Airport. The sculpture will attain local notoriety as Blucifer as the cause of the death of its creator on June 13, 2006. |
| 2008 | January 2 | EchoStar Communications Corporation of Englewood splits into EchoStar Corporation and Dish Network Corporation. |
| 2007 | November 6 | The City of Castle Pines North incorporates. |
| 2007 | October 28 | The Boston Red Sox defeat the Colorado Rockies in four games to win the 2007 World Series. |
| 2007 | October 15 | The Colorado Rockies defeat the Arizona Diamondbacks in four games to win their first National League Pennant. |
| 2007 | August | The Anschutz Medical Campus of the University of Colorado Denver opens. |
| 2007 | July 12 | The United States Fish and Wildlife Service establishes the Rocky Flats National Wildlife Refuge. |
| 2007 | April 27 | The United States National Park Service establishes the Sand Creek Massacre National Historic Site, commemorating the Sand Creek Massacre on November 29, 1864. |
| 2007 | April 7 | The Colorado Rapids defeat D.C. United 2 to 1 in their first game played in the new Dick's Sporting Goods Park. |
| 2007 | January 9 | Bill Ritter assumes office as the forty-first Governor of the State of Colorado. |
| 2006 | November 17 | The T-REX Project in southeast metropolitan Denver is completed 22 months ahead of schedule. |
| 2006 | November 7 | Voters approve an amendment to the Constitution of the State of Colorado banning same-sex marriage. |
| 2006 | October 7 | The Frederic C. Hamilton Building of the Denver Art Museum opens. |
| 2006 | July 28 | The North American Aerospace Defense Command (NORAD) moves the operations of the Cheyenne Mountain Complex to Peterson Air Force Base. |
| 2006 | June 13 | Sculptor Luis A. Jiménez, Jr. is killed in his Hondo, New Mexico studio assembling his Blue Mustang sculpture intended for Denver International Airport. |
| 2006 | May 20 | The Denver Outlaws defeat the Chicago Machine 24 to 14 in their first Major League Lacrosse game. |
| 2006 | May 13 | The Colorado Mammoth defeat the Buffalo Bandits 16 to 9 to win their first National Lacrosse League Champion's Cup. |
| 2005 | December 10 | Professor John L. Hall of the University of Colorado Boulder, Theodor W. Hänsch, and Roy J. Glauber receive the 2005 Nobel Prize in Physics. |
| 2005 | June 13 | The Cussler Museum opens in Arvada. |
| 2005 | June | The Lawrence Argent sculpture I See What You Mean, locally known as the Blue Bear, is erected outside the Colorado Convention Center in Denver. The sculpture will become a beloved symbol of Denver. |
| 2005 | January 1 | An Act of Congress changes the name of the Colorado Canyons National Conservation Area to the McInnis Canyons National Conservation Area. |
| 2004 | November 2 | U.S. President George W. Bush defeats Colorado native John Kerry in the 2004 U.S. presidential election. |
| 2004 | September 24 | U.S. President George W. Bush signs An Act to provide for the establishment of the Great Sand Dunes National Park and Preserve and the Baca National Wildlife Refuge in the State of Colorado, and for other purposes, creating Great Sand Dunes National Park and Preserve from Great Sand Dunes National Monument and creating the Baca National Wildlife Refuge. |
| 2004 | June 4 | An irate citizen of Granby goes on a rampage with a self-built armored bulldozer destroying $7,000,000 worth of property before killing himself. |
| 2003 | November 24 | The Northwest Parkway toll road from Broomfield to the intersection of I-25 and E-470 opens to traffic. |
| 2003 | July 21 | John Hickenlooper is inaugurated as the 43rd Mayor of the City and County of Denver. |
| 2003 | April 8 | The United States Fish and Wildlife Service establishes the Baca National Wildlife Refuge. |
| 2003 | January 3 | The last segment of the E-470 toll road opens to traffic. |
| 2002 | December 4 | U.S. President George W. Bush signs An Act to amend the National Trails System Act to designate the Old Spanish Trail as a National Historic Trail, creating the Old Spanish National Historic Trail. |
| 2002 | June 9 | The Missionary Ridge Fire starts burning in the mountains north of Durango. The wildfire will kill one firefighter and burn 46 homes and 71,739 acres (290 km$^2$) of forest. |
| 2002 | June 8 | A U.S. Forest Service technician ignites the Hayman Fire in the mountains of central Colorado. The wildfire will burn 133 homes, 467 outbuildings, and 137,760 acres (557 km$^2$) of forest, the most in Colorado recorded history. |
| 2002 | April 22 | Linda Lovelace (née Linda Susan Boreman), former pornographic film actor and anti-pornography activist, dies in Denver following an automobile accident. |
| 2001 | December 10 | Professor Eric Allin Cornell of the University of Colorado Boulder, Carl Wieman, and Wolfgang Ketterle receive the 2001 Nobel Prize in Physics. |
| 2001 | November 15 | The Colorado General Assembly creates the City and County of Broomfield from portions of Boulder, Adams, Jefferson, and Weld counties. |
| 2001 | June | Construction on the T-REX Project in southeast metropolitan Denver begins. |
| 2001 | June 9 | The Colorado Avalanche defeat the New Jersey Devils in seven games to win their second Stanley Cup. |
| 2001 | January 1 | Denver celebrates the arrival of the Third Millennium with fireworks above the 16th Street Mall after canceling last year's celebrations for safety concerns. |
| 2000 | October 24 | U.S. President Bill Clinton signs an act of Congress creating the Colorado Canyons National Conservation Area and the Black Ridge Canyons Wilderness. |
| 2000 | October 1 | The State of Colorado transfers Buckley Air National Guard Base back to the United States Air Force as Buckley Air Force Base. |
| 2000 | August 21 | Xcel Energy Inc. is formed by the merger of New Century Energies, Inc. of Denver into the smaller Northern States Power Company. |
| 2000 | June 30 | US West, Inc. of Denver merges into the smaller Qwest Communications International, Inc., also of Denver. |
| 2000 | June 9 | U.S. President Bill Clinton issues a proclamation creating Canyons of the Ancients National Monument. |
| 2000 | May 9 | The Denver Museum of Natural History changes its name to the Denver Museum of Nature and Science. |
| 2000 | April 7 | The American Association of State Highway and Transportation Officials (AASHTO) approves the extension of the Interstate Highway I-270 designation from I-76 northwest to the intersection of I-25 and US 36. |
| 2000 | April 1 | The 2000 United States census enumerates the population of the State of Colorado, later determined to be 4,301,262, an increase of 30.56% since the 1990 United States census. Colorado becomes the 24th most populous of the 50 U.S. states and will gain a 7th Congressional District. |

### 1990s

| Year | Date | Event |
| 1999 | October 21 | U.S. President Bill Clinton signs An Act to redesignate the Black Canyon of the Gunnison National Monument as a national park and establish the Gunnison Gorge National Conservation Area, and for other purposes, creating Black Canyon of the Gunnison National Park and the Gunnison Gorge National Conservation Area. |
| 1999 | April 20 | The Columbine High School massacre begins when Eric Harris and Dylan Klebold open fire on the Columbine High School campus in Jefferson County killing 12 students and a teacher and wounding 24 others before killing themselves. |
| 1999 | January 31 | The Denver Broncos defeat the Atlanta Falcons 34 to 19 in Super Bowl XXXIII. Quarterback John Elway wins his second consecutive Super Bowl and his 148th NFL game, and is named the Super Bowl Most Valuable Player. |
| 1999 | January 17 | The Denver Broncos defeat the New York Jets 23 to 10 to become the first team to win the American Football Conference Championship six times. |
| 1999 | January 12 | Bill Owens assumes office as the 40th Governor of the State of Colorado. |
| 1998 | October 12 | Matthew Shepard dies at Poudre Valley Hospital in Fort Collins six days after a savage beating and robbery in Laramie, Wyoming. |
| 1998 | June 5 | The United States Air Force renames Falcon Air Force Base as Schriever Air Force Base. |
| 1998 | January 25 | The Wild Card Denver Broncos defeat the world champion Green Bay Packers 31 to 24 in Super Bowl XXXII. Terrell Davis is named the Super Bowl Most Valuable Player. |
| 1998 | January 11 | The Wild Card Denver Broncos defeat the Pittsburgh Steelers 24 to 21 to win the American Football Conference Championship for the fifth time. |
| 1997 | August 13 | The animated television series South Park debuts. The series set in the fictional town of South Park, Colorado in the real mountain basin of South Park, will become the longest running TV series with a Colorado setting. |
| 1997 | August 1 | New Century Energies, Inc. of Denver is formed by the merger of Southwestern Public Service Company with the larger Public Service Company of Colorado. |
| 1997 | July 17 | A Lakewood boy is killed by a mountain lion while hiking with his family in Rocky Mountain National Park. |
| 1997 | June 20 | The Group of Eight's 23rd annual meeting convenes in Denver. |
| 1997 | January 3 | Diana DeGette of Denver succeeds Congresswoman Pat Schroeder in the United States House of Representatives. |
| 1996 | December 26 | The body of JonBenét Ramsey is found in the basement of her home in Boulder. |
| 1996 | September 11 | The Southern Pacific Transportation Company merges with the UP Holding Company, Inc. to form the Union Pacific Corporation. The Southern Pacific Railroad becomes part of the Union Pacific Railroad. |
| 1996 | July 22 | Amy Van Dyken of Englewood wins the first of her six Olympic gold medals in swimming at the Games of the XXVI Olympiad in Atlanta. |
| 1996 | June 11 | The Colorado Avalanche defeat the Florida Panthers in four games to win their first Stanley Cup, becoming the first major league sports team to bring a championship trophy to Colorado. |
| 1996 | May 20 | The United States Supreme Court rules in Romer v. Evans that Colorado Amendment 2 approved in 1992 violates the United States Constitution. |
| 1996 | April 13 | The Colorado Rapids lose to Sporting Kansas City 3 to 0 in their first Major League Soccer game. |
| 1995 | December 28 | EchoStar Communications Corporation of Englewood successfully launches its first satellite, EchoStar I. |
| 1995 | October 6 | The Colorado Avalanche defeat the Detroit Red Wings 3 to 2 in their first game since relocation. |
| 1995 | June 11 | Denver International Airport opens replacing Stapleton International Airport. |
| 1995 | April 26 | The Colorado Rockies defeat the New York Mets 11 to 9 in the first game played in the new Coors Field. |
| 1995 | March 25 | The Michael Graves designed addition to the central Denver Public Library opens. |
| 1994 | December 15 | The Town of Foxfield incorporates. |
| 1994 | December 10 | Rashaan Salaam of the University of Colorado Buffaloes football team wins the 1994 Heisman Trophy. |
| 1994 | October 7 | The Regional Transportation District begins light rail service in Denver. |
| 1994 | July 6 | A blowup of the South Canyon Fire kills 14 wildlands firefighters on Storm King Mountain, near Glenwood Springs. |
| 1993 | December 15 | Colorado district judge Jeffrey Bayless rules that Colorado Amendment 2 violates the United States Constitution. |
| 1993 | September 15 | The interchange of I-76 with I-25 is opened, completing the extended 188.10-mile (302.72 km) length of Interstate Highway I-76 in Colorado. This project completes the original design of the Interstate Highway System in Colorado, although improvements and enhancements will continue. |
| 1993 | August 10 | Pope John Paul II arrives in Denver to celebrate World Youth Day. This is the first visit to Colorado by a pope. |
| 1993 | August 10 | A Fremont County man is killed by a black bear in his trailer. |
| 1993 | April | Construction begins to directly connect the intersection of I-270 and I-76 with the intersection of I-25 and US 36. |
| 1993 | April 9 | The Colorado Rockies defeat the Montreal Expos 14 to 4 in their very first home game. |
| 1993 | April 5 | The Colorado Rockies lose their very first game to the New York Mets 3 to 0. |
| 1993 | July 13 | Steve Ells opens the first Chipotle Mexican Grill at 1644 East Evans Avenue in Denver. |
| 1992 | November 3 | Voters approve Colorado Amendment 2 to the state constitution which prohibits "special rights" based upon sexual orientation. Amendment 2 never takes effect due to legal challenges. |
| 1992 | November 3 | Voters approve Colorado Amendment 1 to the state constitution, also known as the Colorado Taxpayer Bill of Rights (TABOR). |
| 1992 | October 14 | Governor Roy Romer dedicates the segment of I-70 through Glenwood Canyon, completing the extended 449.589-mile (723.543 km) length of Interstate Highway I-70 through Colorado. |
| 1992 | October 9 | U.S. President George H. W. Bush signs an act of Congress creating the Rocky Mountain Arsenal National Wildlife Refuge. |
| 1992 | August 3 | U.S. President George H. W. Bush signs an Act to amend the National Trails System Act to designate the California National Historic Trail and Pony Express National Historic Trail as components of the National Trails System. |
| 1992 | May 26 | U.S. President George H. W. Bush signs an act of Congress creating the Two Ponds National Wildlife Refuge. |
| 1991 | October 15 | Giant Records releases the Warren Zevon album Mr. Bad Example including the song "Things to Do in Denver When You're Dead". |
| 1991 | September 16 | U.S. President George H. W. Bush announces the promotion of the Solar Energy Research Institute to the National Renewable Energy Laboratory (NREL), a national laboratory of the United States Department of Energy. |
| 1991 | July 15 | Wellington Webb is inaugurated as the first African-American and 42nd Mayor of the City and County of Denver. |
| 1991 | June | The first segment of the E-470 toll road opens to traffic. |
| 1991 | January 14 | An Idaho Springs man is killed by a mountain lion on a trail near his home. |
| 1991 | January 1 | The University of Colorado Buffaloes football team defeat the University of Notre Dame Fighting Irish 10 to 9 to win the Orange Bowl and the Associated Press National Championship Trophy. |
| 1990 | November 26 | The United States Army transfers the Piñon Canyon Maneuver Site to Comanche National Grassland. |
| 1990 | November 24 | The U.S. Environmental Protection Agency vetoes the Two Forks Dam Project proposed by the Denver Board of Water Commissioners. |
| 1990 | November 7 | The Colorado Fuel & Iron company in Pueblo files for Chapter 11 bankruptcy protection. |
| 1990 | June 23 | The Colorado Convention Center opens in Denver. |
| 1990 | April 1 | The 1990 United States census enumerates the population of the State of Colorado, later determined to be 3,294,394, an increase of 13.99% since the 1980 United States census. Colorado becomes the 26th most populous of the 50 U.S. states. |
| 1990 | January 28 | The San Francisco 49ers defeat the Denver Broncos 55 to 10 in Super Bowl XXIV. |
| 1990 | January 14 | The Denver Broncos defeat the Cleveland Browns 37 to 21 to win the American Football Conference Championship for the fourth time. |

### 1980s

| Year | Date | Event |
| 1989 | December 10 | Professor Thomas Cech of the University of Colorado Boulder and Sidney Altman receive the 1989 Nobel Prize in Chemistry. |
| 1989 | November 22 | The City and County of Denver holds a ground-breaking ceremony for a new airport to replace the aging Stapleton International Airport. |
| 1989 | June 6 | The Federal Bureau of Investigation and the Environmental Protection Agency raid the Department of Energy Rocky Flats Plant near Arvada. |
| 1988 | November 8 | Voters in Adams, Arapahoe, Boulder, Denver, Douglas, and Jefferson counties approved the creation of the Scientific and Cultural Facilities District. |
| 1988 | October 13 | The Denver and Rio Grande Western Railroad becomes part of the Southern Pacific Railroad when Rio Grande Industries, Inc. acquires the Southern Pacific Transportation Company. |
| 1988 | June 18 | The United States Air Force renames Falcon Air Force Station as Falcon Air Force Base. |
| 1988 | January 31 | The Washington Redskins defeat the Denver Broncos 42 to 10 in Super Bowl XXII. |
| 1988 | January 17 | The Denver Broncos defeat the Cleveland Browns 38 to 33 to win the American Football Conference Championship for the third time. |
| 1987 | May 8 | U.S. President Ronald Reagan signs An Act to amend the National Trails System Act to designate the Santa Fe Trail as a National Historic Trail, creating the Santa Fe National Historic Trail. |
| 1987 | May 8 | U.S. Senator Gary Hart announces the end of his presidential campaign which began the previous month. |
| 1987 | April 5 | The National Mining Hall of Fame and Museum opens in Leadville. |
| 1987 | January 13 | Roy Romer assumes office as the thirty-ninth Governor of the State of Colorado. |
| 1987 | January 25 | The New York Giants defeat the Denver Broncos 39 to 20 in Super Bowl XXI. |
| 1987 | January 11 | The Denver Broncos defeat the Cleveland Browns 23 to 20 in overtime to win the American Football Conference Championship for the second time. The Drive becomes a part of American football lore. |
| 1985 | September 26 | The United States Air Force opens the Consolidated Space Operations Center at Falcon Air Force Station near Colorado Springs. |
| 1985 | February 1 | An ambient air temperature of −61 °F (−51.7 °C) at Maybell sets the official Colorado all-time low temperature record. |
| 1984 | November | The Anschutz Corporation acquires Rio Grande Industries for $500 million. The new Rio Grande Holdings, Inc. includes the Denver and Rio Grande Western Railroad. |
| 1984 | August 1 | A truck carrying six torpedoes for the United States Navy overturns and dumps its potentially explosive load into the intersection of I-25 and I-70 in Denver, the busiest intersection in Colorado known locally as the Mousetrap. |
| 1984 | July 22 | Marianne Martin of Boulder wins the first Tour de France féminin with a time of 29:39:02. |
| 1984 | June 18 | Alan Berg is murdered at his home in Denver by members of The Order. |
| 1984 | February 16 | Scott Hamilton wins the Olympic gold medal in Men's Figure Skating at the XIV Olympic Winter Games in Sarajevo. |
| 1984 | January 1 | US West, Inc. of Denver is formed by the Bell System divestiture as a holding company with Mountain States Telephone and Telegraph (dba Mountain Bell), Northwestern Bell Telephone Company (dba Northwestern Bell), and Pacific Northwest Bell Telephone Company (dba Pacific Northwest Bell). |
| 1983 | July 2 | Federico Peña is inaugurated as the first Hispanic and 41st Mayor of the City and County of Denver. |
| 1983 | June 5 | The Irish band U2 performs at the Red Rocks Amphitheatre in a concert recorded as U2 Live at Red Rocks: Under a Blood Red Sky. |
| 1983 | May 17 | The United States Air Force begins construction of Falcon Air Force Station near Colorado Springs. |
| 1982 | December 28 | Congressman-elect and former astronaut Jack Swigert of Littleton dies in Washington, D.C. at age 51. |
| 1982 | October 4 | The 16th Street Mall in Denver opens. |
| 1982 | June 4 | The American Homebrewers Association sponsors the first Great American Beer Festival at its Fourth Annual Conference in Boulder. |
| 1982 | April 3 | The Colorado Rockies defeat the Calgary Flames 3 to 1 in their final National Hockey League game. In their six NHL seasons, the Rockies compiled a record of 113 wins, 283 losses, and 86 ties. |
| 1981 | October 1 | The annexation of the Broadmoor, Skyway, Ivywild, Cheyenne Canon, and Stratton Meadows neighborhoods by the City of Colorado Springs is upheld by the Colorado Supreme Court after a District Court voided the annexation. |
| 1981 | January 12 | The television series Dynasty debuts. The series will become the longest running non-animated TV series set in Colorado (8 seasons, c.f. Dr. Quinn, Medicine Woman 6 sessions, Mork & Mindy 4 sessions). |
| 1980 | December 9 | Charlie Ergen, Jim DeFranco, and Cantey McAdams form EchoSphere in Littleton. |
| 1980 | April 1 | The 1980 United States census enumerates the population of the State of Colorado, later determined to be 2,889,964, an increase of 30.93% since the 1970 United States census. Colorado becomes the 28th most populous of the 50 U.S. states and will gain a 6th Congressional District. |

### 1970s

| Year | Date | Event |
| 1979 | December 25 | Pope John Paul II grants the Cathedral of the Immaculate Conception in Denver the title Basilica minor. |
| 1979 | December 21 | Governor Dick Lamm dedicates the Edwin C. Johnson Bore of the Eisenhower–Johnson Memorial Tunnel completing the section of Interstate Highway 70 under the Continental Divide. |
| 1979 | November 1 | Congressman Ken Kramer leaks the location selected for the Consolidated Space Operations Center east of Colorado Springs. |
| 1978 | November 10 | U.S. President Jimmy Carter signs the National Parks and Recreation Act of 1978 authorizing the Continental Divide National Scenic Trail, the Mormon Pioneer National Historic Trail, and the Oregon National Historic Trail. |
| 1978 | October 11 | U.S. President Jimmy Carter signs An Act to create the Indian Peaks Wilderness Area and the Arapaho National Recreation Area, to authorize the Secretary of the Interior to study the feasibility of revising the boundaries of the Rocky Mountain National Park, and to add certain lands to the Oregon Islands Wilderness, creating the Indian Peaks Wilderness Area and the Arapaho National Recreation Area. |
| 1978 | October 9 | The United Nations Educational, Scientific and Cultural Organization (UNESCO) designates Mesa Verde National Park as one of the first 12 World Heritage Sites. |
| 1978 | September 14 | The comedy television series Mork & Mindy, set in Boulder, debuts. |
| 1978 | August | The Town of Avon incorporates. |
| 1978 | August 1 | The United States Olympic Committee moves into its new headquarters at the United States Olympic Training Center in Colorado Springs. |
| 1978 | | U.S. Highway 36 is extended westward along State Highway 66 from Estes Park to Deer Ridge Junction in Rocky Mountain National Park. |
| 1978 | February 26 | Boettcher Concert Hall of the Denver Center for the Performing Arts opens in the Denver Performing Arts Complex. |
| 1978 | January 15 | The Dallas Cowboys defeat the Denver Broncos 20 to 17 in Super Bowl XII. |
| 1978 | January 1 | The Denver Broncos defeat the Oakland Raiders 20 to 17 to win their first American Football Conference Championship. |
| 1977 | September 30 | Proposed Colorado Interstate Highway I-470 is withdrawn from the Interstate Highway System. |
| 1977 | July 28 | Governor Dick Lamm requests that the proposed 26.3-mile (42.3 km) Colorado Interstate Highway I-470 be withdrawn from the Interstate Highway System. |
| 1977 | July 5 | The United States Department of Energy opens the Solar Energy Research Institute (SERI) in Golden. |
| 1977 | June | The United States Olympic Training Center at the former Ent Air Force Base in Colorado Springs opens to athletes. |
| 1976 | October 22 | The Denver Nuggets defeat the Indiana Pacers 123 to 110 in their first game as a National Basketball Association franchise. |
| 1976 | October 5 | The Colorado Rockies defeat the Toronto Maple Leafs 4 to 2 in their first National Hockey League game since relocation. |
| 1976 | October 1 | Ent Air Force Base closes in Colorado Springs. |
| 1976 | August 1 | A somber State of Colorado observes its centennial as it assesses the damage from the Big Thompson Flood the previous evening. |
| 1976 | July 31 | A flash flood in Big Thompson Canyon kills 143 people just hours before the Colorado State Centennial. |
| 1976 | July 4 | The State of Colorado celebrates the Bicentennial of the United States of America. |
| 1976 | May 21 | The final segment of I-225 is opened in Denver, completing the entire 11.959-mile (19.246 km) length of Interstate Highway I-225. |
| 1976 | May 13 | The New York Nets defeat the Denver Nuggets 112 to 106 in the last American Basketball Association game ever played. The Denver Rockets/Nuggets finish their nine seasons in the ABA with a record of 474 wins and 432 losses. |
| 1976 | March 1 | The United States Air Force renames Peterson Field in Colorado Springs as Peterson Air Force Base. |
| 1975 | August 18 | Construction of the second bore of the Eisenhower Tunnel begins. |
| 1975 | April 1 | Ent Air Force Base is downgraded to the Ent Annex of the Cheyenne Mountain Air Force Station. |
| 1975 | January 14 | Dick Lamm assumes office as the thirty-eighth Governor of the State of Colorado. |
| 1974 | December 21 | The first Telluride Film Festival begins. |
| 1974 | October 16 | The Denver Nuggets lose to the Kentucky Colonels 117 to 99 in their first game since the team name was changed from the Denver Rockets. |
| 1974 | August 1 | Interstate highway I-80S is redesignated I-76. Over 500 route markers will be replaced in Colorado over the next two years. |
| 1974 | | The United States Army renames Fitzsimons Army Hospital in Aurora as Fitzsimons Army Medical Center. |
| 1974 | | Chogyam Trungpa establishes the Naropa Institute in Boulder. |
| 1974 | April | The City of Cañon City annexes the Town of East Cañon. |
| 1974 | March | Reprise Records releases the Bob Seger album Seven including the song "Get out of Denver". |
| 1973 | December 9 | The Denver Broncos defeat the San Diego Chargers 42 to 28 to assure their first winning season in their 14th year of play. |
| 1973 | September 8 | Rebecca Ann King of Denver is crowned Miss America. |
| 1973 | July 16 | Lieutenant Governor John Vanderhoof assumes office as the thirty-seventh Governor of the State of Colorado upon the resignation of Governor John Love to serve as Director of the United States Office of Energy Policy. |
| 1973 | June 21 | The United States Supreme Court orders the complete desegregation of the Denver Public Schools in Keyes v. School District No. 1. |
| 1973 | May 17 | The United States Atomic Energy Commission detonates three underground nuclear explosions in Colorado. Project Rio Blanco used the three nearly simultaneous blasts, each equivalent to 33,000 tonnes of TNT, to determine if nuclear explosions could be used to extract natural gas from sandstone deposits. |
| 1973 | March 8 | Governor John Love dedicates the first bore of the Eisenhower Tunnel taking Interstate 70 under the Continental Divide of the Americas, the highest point on the Interstate Highway System. |
| 1973 | January 3 | Pat Schroeder of Denver takes her seat in the United States House of Representatives as Colorado's first woman delegate to the U.S. Congress. Congresswoman Schroeder will represent Colorado's 1st congressional district for 24 years. |
| 1972 | November 15 | Denver withdraws its offer to host the 1976 Winter Olympics, the first and only host city to reject an awarded Olympic Games. |
| 1972 | November 7 | Colorado voters reject a $5 million bond issue to fund the 1976 Winter Olympics. |
| 1972 | September 10 | Frank Shorter of Boulder wins the Men's Marathon at the Games of the XX Olympiad in Munich. |
| 1971 | October 3 | The United States Department of Transportation opens the High Speed Ground Test Center east of Pueblo. |
| 1971 | May 19 | The Denver Art Museum opens its Gio Ponti designed North Tower. |
| 1970 | October 23 | The final segment of I-270 is opened, completing the 5.2-mile (8.4 km) Interstate Highway I-270. |
| 1970 | September 20 | The Denver Broncos defeat the Buffalo Bills 25 to 10 in their first game as a National Football League franchise. |
| 1970 | April 13 | An oxygen tank exploded on the Apollo 13 space flight to the Moon. The three-man crew, including Command Module Pilot Jack Swigert of Denver, managed to fly safely back to Earth four days later. |
| 1970 | April 1 | The 1970 United States census enumerates the population of the State of Colorado, later determined to be 2,207,259, an increase of 25.85% since the 1960 United States census. Colorado becomes the 30th most populous of the 50 U.S. states and will gain a 5th Congressional District. |

### 1960s

| Year | Date | Event |
| 1969 | December 14 | The Denver Broncos defeat the Cincinnati Bengals 27 to 16 in their last game as an American Football League franchise. The Broncos finish the ten AFL seasons with a record of 39 wins, 97 losses, and 4 ties. |
| 1969 | October | The John Denver debut album Rhymes & Reasons is released. |
| 1969 | September 21 | The final 21-mile (34 km) segment of Interstate Highway I-25 south of Walsenburg opens to traffic, completing the entire 305.040-mile (490.914 km) length of I-25 in Colorado. |
| 1969 | September 10 | The United States Atomic Energy Commission detonates the first nuclear explosion in Colorado. Project Rulison used the underground blast, equivalent to 40,000 tonnes of TNT, to determine if nuclear explosions could be used to extract natural gas from shale gas deposits. |
| 1969 | August 20 | U.S. President Richard Nixon signs An Act to provide for the establishment of the Florissant Fossil Beds National Monument in the State of Colorado. |
| 1969 | August 20 | The City of Wheat Ridge in eastern Jefferson County incorporates. |
| 1969 | July 1 | The Colorado General Assembly creates the Regional Transportation District to promote public transportation in the Denver metropolitan area. |
| 1969 | June 24 | The City of Lakewood in eastern Jefferson County incorporates. |
| 1969 | May 27 | The United States Department of Agriculture creates Comanche National Grassland and Pawnee National Grassland. |
| 1969 | May 12 | The International Olympic Committee selects Denver to host the XII Olympic Winter Games in 1976. |
| 1969 | May 11 | A plutonium fire in Building 776/777 of the Atomic Energy Commission Rocky Flats Plant contaminates the plant near Arvada in the most expensive U.S. industrial accident to date. |
| 1968 | December 31 | Deputy Major William H. McNichols, Jr. assumes office as the 40th Mayor of the City and County of Denver replacing Tom Currigan. |
| 1968 | December 13 | United States Secretary of Transportation Alan Boyd announces the selection of 1,472.5 miles (2369.8 km) of additional highway routes for the Interstate Highway System, including the 5.6-mile (9.0 km) extension of Interstate Highway I-80S from I-25 to I-70. |
| 1968 | December 2 | U.S. President Lyndon B. Johnson signs An Act to establish a national trails system, and for other purposes, creating the National Trails System. |
| 1968 | March 15 | Construction begins on the first bore of the Straight Creek Tunnel designed to route Interstate Highway I-70 under the Continental Divide. |
| 1968 | February 10 | Peggy Fleming wins the Olympic gold medal in Women's Figure Skating at the X Olympic Winter Games in Grenoble. |
| 1967 | October 15 | The Denver Rockets defeat the Anaheim Amigos 110 to 105 in their first game in the new American Basketball Association. |
| 1967 | September 17 | The Denver-Boulder Turnpike becomes the first public toll road in the United States to pay for itself and becomes a freeway. The turnpike becomes a portion of the westward extension of federal highway route US-36 from Denver to Estes Park. |
| 1967 | September 5 | The United States Fish and Wildlife Service establishes the Arapaho National Wildlife Refuge. |
| 1967 | August 5 | The Denver Broncos defeat the Detroit Lions 13 to 7 to become the first American Football League team to defeat a National Football League team. |
| 1966 | October 19 | Blue Mesa Dam on the Gunnison River in Gunnison County is completed. |
| 1966 | January 1 | Air Force Systems Command turned the Cheyenne Mountain Combat Operations Center over to NORAD. |
| 1965 | December 12 | Interstate Highway I-270 construction begins in Denver. |
| 1965 | July 25 | The United States Fish and Wildlife Service establishes the Browns Park National Wildlife Refuge. |
| 1965 | June 16 | A flash flood on the South Platte River kills 28 people and inflicts over $500 million in damage. |
| 1965 | March 26 | The last Titan I ICBM of the former Lowry Bombing and Gunnery Range was taken off alert status (all Titan 1s were in storage by April 18). |
| 1965 | February 6 | The National Park Service creates the Curecanti National Recreation Area. |
| 1964 | August 26 | The British band The Beatles perform at Red Rocks Amphitheatre near Morrison. |
| 1964 | July 3 | The Robert Ward opera The Lady from Colorado premieres at the Central City Opera. |
| 1964 | June 11 | The musical film The Unsinkable Molly Brown premieres in Denver. |
| 1964 | May | Construction of Interstate Highway I-225 begins in Aurora. |
| 1964 | | Stapleton Airfield in Denver is renamed Stapleton International Airport. |
| 1963 | December | Dillon Dam on the Blue River in Summit County is completed. |
| 1963 | September | Eminent nuclear physicist Edward Condon joins the faculty of the University of Colorado. |
| 1963 | July 25 | The United States Fish and Wildlife Service establishes the Alamosa National Wildlife Refuge. |
| 1963 | March 1 | Dr. Thomas Starzl performs the world's first liver transplant at the University of Colorado Hospital in Denver. |
| 1963 | January 8 | John Love assumes office as the thirty-sixth Governor of the State of Colorado. |
| 1962 | November 15 | Three Atlas missile sites of Warren Air Force Base begin operation in Colorado (eventually 8 sites at Keoto, 5 at Padroni, 8 at Peetz, 8 at Stoneham, etc.) |
| 1962 | May 24 | Astronaut Scott Carpenter from Boulder becomes the fourth person to orbit the Earth. |
| 1962 | April 24 | The first of a series of minor earthquakes emanating from a region below the United States Army Rocky Mountain Arsenal near Denver is recorded. The earthquakes are later tied to the injection of toxic fluids into a hazardous waste disposal well at the chemical weapons plant. |
| 1962 | April 16 | United States Deputy Attorney General Byron White is appointed the 83rd Associate Justice of the Supreme Court of the United States. White will serve on the court for 31 years. |
| 1961 | July 20 | Tunneling begins for the NORAD bunker (the plan for a Denver Sector bunker had been cancelled in 1959, and the SAC bunker near Cripple Creek planned for 1965 was cancelled in 1963.) |
| 1961 | June | The Town of Broomfield incorporates. |
| 1960 | November 3 | The Meredith Willson musical The Unsinkable Molly Brown opens at the Winter Garden Theatre. |
| 1960 | September 9 | The Denver Broncos defeat the Boston Patriots 13 to 10 in the very first American Football League game. |
| 1960 | August 3 | Dave Rearick and Bob Kamps become the first climbers to surmount The Diamond on the east face of Longs Peak. |
| 1960 | June 3 | U.S. President Dwight D. Eisenhower signs An Act Authorizing the establishment of a national historic site at Bent's Old Fort, near La Junta, Colorado, creating Bent's Old Fort National Historic Site. |
| 1960 | spring | Interstate 70 in Colorado construction begins near Idaho Springs. |
| 1960 | April 1 | The 1960 United States census enumerates the population of the State of Colorado, later determined to be 1,753,947, an increase of 32.36% since the 1950 United States census. Colorado becomes the 33rd most populous of the 50 U.S. states. |
| 1960 | February 9 | Brewer Adolph Coors III is murdered in a foiled kidnap attempt near his home in Bear Creek Canyon west of Denver. |

### 1950s

| Year | Date | Event |
| 1959 | July 2 | The Town of Columbine Valley incorporates. |
| 1959 | June 3 | The first class of the United States Air Force Academy graduates. |
| 1959 | September 1 | Lowry Missile Site Number 1 construction begins southeast of Denver for a Titan I launch complex--Martin Missile Test Site 1 construction at Waterton Canyon had begun in April (alert status ended on March 26, 1965). |
| 1959 | January 22 | The Adolf Coors Company of Golden introduces the aluminum beer can. |
| 1958 | December 10 | Edward Lawrie Tatum is the 1st Colorado native to win the Nobel Prize for his 1937 metabolism work at Stanford University with George Wells Beadle. |
| 1958 | August | The Town of Bow Mar incorporates. |
| 1958 | August | Construction of Interstate Highway I-80S begins in northeastern Colorado (designated I-76 on August 1, 1974.) |
| 1958 | May 12 | Canada and the United States establish the North American Air Defense Command (NORAD) to be headquartered at Ent Air Force Base. |
| 1957 | October 18 | United States Secretary of Commerce Sinclair Weeks announces a 547-mile (880 km) western extension of Interstate 70 from Interstate 25 in Denver to Interstate 15 in Utah. The highway extension will require burrowing under the Continental Divide of the Americas. |
| 1957 | September 11 | A plutonium fire in Building 71 of the Atomic Energy Commission Rocky Flats Plant contaminates the plant and releases radioactive plutonium into the air near Denver. |
| 1957 | January 8 | Steve McNichols assumes office as the thirty-fifth Governor of the State of Colorado. |
| 1956 | November 10 | Professor George Gamow (Георгий Антонович Гамов) of the University of Colorado is awarded the 1956 UNESCO Kalinga Prize. |
| 1956 | October 15 | The Denver Public Library dedicates the new central library at the Denver Civic Center |
| 1956 | September 22 | The Town of Boone incorporates. |
| 1956 | July 7 | The Douglas Moore opera The Ballad of Baby Doe premieres at the Central City Opera. |
| 1955 | November | Monument Valley Freeway construction begins in Colorado Springs (later incorporated as part of I-25). |
| 1955 | September 24 | U.S. President Dwight Eisenhower suffers an acute myocardial infarction in Denver. The President is treated at Fitzsimons Army Hospital in Aurora for several weeks. |
| 1955 | September 11 | Sharon Kay Ritchie is the 1st Miss Colorado crowned Miss America (cf. Marilyn Van Derbur in 1957, Rebecca Ann King in 1973). |
| 1955 | July 11 | The first class of 306 cadets of the United States Air Force Academy are sworn in at Lowry Air Force Base in Denver. |
| 1955 | January 11 | Ed Johnson assumes office again as the thirty-fourth Governor of the State of Colorado. |
| 1955 | January 3 | Gordon L. Allott takes his seat in the United States Senate. He will serve as a U.S. Senator from Colorado for 18 years. |
| 1954 | June 24 | The United States Air Force selects an area north of Colorado Springs as the site for the United States Air Force Academy. |
| 1953 | June 15 | The Town of Fraser incorporates. |
| 1953 | spring | The Summer White House for U.S. President Dwight Eisenhower is established at Lowry Air Force Base through 1955. |
| 1952 | December 18 | The Town of Commerce incorporates. |
| 1952 | September 3 | The United States Fish and Wildlife Service establishes the Monte Vista National Wildlife Refuge. |
| 1952 | July 18 | Denver television station KFEL-TV (analog channel 2) begins the first television broadcasts in Colorado. |
| 1952 | May 19 | The Town of Glendale incorporates. |
| 1952 | January 19 | The Denver-Boulder Turnpike opens to traffic. |
| 1951 | July 10 | Construction of the United States Atomic Energy Commission Rocky Flats Plant begins 15 miles (24 km) northwest of Denver. |
| 1951 | January 9 | Dan Thornton assumes office as the thirty-third Governor of the State of Colorado. |
| 1951 | January 3 | Byron G. Rogers of Denver takes his seat in the United States House of Representatives. Congressman Rogers will represent Colorado's 1st congressional district for 20 years. |
| 1950 | August 28 | U.S. President Harry S. Truman issues a Public Land Order creating Manti-La Sal National Forest. |
| 1950 | August 3 | U.S. President Harry S. Truman signs An Act to abolish the Wheeler National Monument, in the State of Colorado, and to provide for the administration of the lands contained therein as a part of the national forest within which such national monument is situated, and for other purposes. The monument becomes the Wheeler Geologic Area of Rio Grande National Forest, and will become a part of the La Garita Wilderness. |
| 1950 | August 3 | U.S. President Harry S. Truman signs An Act to abolish the Holy Cross National Monument, in the State of Colorado, and to provide for the administration of the lands contained therein as a part of the national forest within which such national monument is situated, and for other purposes. The monument reverts to White River National Forest, and will become a part of the Holy Cross Wilderness. |
| 1950 | April 15 | Lieutenant Governor Walter Johnson assumes office as the thirty-second Governor of Colorado upon the resignation of Governor Bill Knous to serve as a federal judge. |
| 1950 | April 1 | The 1950 United States census enumerates the population of the State of Colorado, later determined to be 1,325,089, an increase of 17.96% since the 1940 United States census. Colorado becomes the 34th most populous of the 48 U.S. states. |
| 1950 | March 6 | The Town of Campo incorporates. |
| 1950 | February 13 | Aspen hosts the FIS Alpine World Ski Championships 1950 at Ajax Mountain Ski Resort, the first World Ski Championships held outside Europe. |

### 1940s

| Year | Date | Event |
| 1949 | | Construction begins on the Pueblo Freeway in Pueblo. The Pueblo Freeway will be incorporated into Interstate Highway I-25. |
| 1949 | January 3 | Wayne N. Aspinall of Palisade takes his seat in the United States House of Representatives. Congressman Aspinall will represent Colorado's 4th congressional district for 24 years. |
| 1948 | August | Construction begins on the Valley Highway in Denver. The Valley Highway will be incorporated into Interstate Highway I-25. |
| 1948 | March 15 | The Town of Cokedale incorporates. |
| 1947 | | Denver FM radio station KLZ-FM begins commercial broadcasting at 106.7 MHz in the new U.S. FM broadcast band. |
| 1947 | November | Lloyd J. King opens first location of the grocery chain King Soopers in Arvada, Colorado. |
| 1947 | December 9 | The Town of Artesia incorporates. |
| 1947 | January 14 | William Lee Knous assumes office as the thirty-first Governor of the State of Colorado. |
| 1946 | December 14 | The Ajax Mountain Ski Area opens at Aspen with the world's longest chairlift. |
| 1945 | September 10 | Mike the Headless Chicken survives an assassination attempt but loses his head near Fruita. |
| 1945 | September 2 | World War II ends as the Empire of Japan formally surrenders. |
| 1945 | July 19 | The battleship USS Colorado (BB-45) steams into Tokyo Bay for the invasion of Honshu. |
| 1945 | July 19 | The Town of Cherry Hills Village incorporates. |
| 1945 | May 8 | The war in Europe ends as the Greater German Empire formally surrenders. |
| 1945 | spring | The Colorado Springs Tent Camp was established between the east edge of Colorado Springs and Peterson Field. ("Ent Air Force Base" in 1949, "Ent Annex" in 1975). |
| 1945 | January 12 | John Charles Vivian assumes office as the thirtieth Governor of the State of Colorado. |
| 1944 | December 31 | The City and County of Denver annexes the Town of MountainView Park. |
| 1942 | August 27 | The Granada War Relocation Center (Camp Amache) opens for Japanese-American internees (Governor Carr opposed the internments in July.) |
| 1942 | June 30 | Rocky Mountain Arsenal construction begins near Denver for World War II chemical weapons. |
| 1942 | April 28 | The United States Army opens the Army Air Base at the Colorado Springs Municipal Airport (the shared airfield is later designated Peterson Field). |
| 1942 | April | The United States Army begins construction of Camp Hale near Tennessee Pass. |
| 1942 | April | Lowry Field Number 2 construction begins east of Aurora—cantonment construction begins May 5, 1942 (later designated Buckley Field, Buckley Air National Guard Base in 1960, Buckley AFB in 2000). |
| 1942 | January 6 | The United States Army announces the selection of Colorado Springs as the site of a major Army base (designated Camp Carson a few weeks later, Fort Carson on August 27, 1954). |
| 1941 | December 11 | The United States declares war on the German Reich and the Italian Empire |
| 1941 | December 8 | The United States declares war on the Empire of Japan and enters World War II. |
| 1941 | June 15 | Rotary International celebrates the Grand Opening of Red Rocks Amphitheatre with 10,000 in attendance during their annual convention. An "informal dedication" was held the week before. |
| 1941 | April 14 | The Town of East Cañon incorporates. |
| 1941 | March | Denver Ordnance Plant construction begins after a 1940 land purchase and January 1941 contract with Remington Arms Company (cf. February 1942 construction of the Pueblo Ordnance Depot). |
| 1941 | January 3 | Colorado's 2nd congressional district representative (William S. Hill) and Colorado's 3rd congressional district representative (John Chenoweth) are seated in the United States House of Representatives. |
| 1940 | May 19 | The Town of Federal Heights incorporates. |
| 1940 | April 1 | The 1940 United States census enumerates the population of the State of Colorado, later determined to be 1,123,296, an increase of 8.45% since the 1930 United States census. Colorado remains the 33rd most populous of the 48 U.S. states. |

### 1930s

| Year | Date | Event |
| 1939 | June 15 | The Town of Dove Creek incorporates. |
| 1939 | January 10 | Ralph Carr assumes office as the twenty-ninth Governor of the State of Colorado. |
| 1938 | December 2 | U.S. President Franklin D. Roosevelt signs an executive order creating Colorado State Forest. |
| 1938 | July 14 | U.S. President Franklin D. Roosevelt signs an executive order greatly enlarging Dinosaur National Monument. |
| 1937 | October 4 | Lowry Field construction begins with Works Progress Administration conversion of the Agnes Stipps Memorial Sanitorium for an Air Corps training base east of Denver (renamed Lowry AFB June 24, 1948.) |
| 1937 | September 6 | The Will Rogers Shrine of the Sun is dedicated along the 1925 Cheyenne Mountain Highway. |
| 1937 | July 22 | U.S. President Franklin D. Roosevelt signs An Act to create the Farmers' Home Corporation, to promote more secure occupancy of farms and farm homes, to correct the economic instability resulting from some present forms of farm tenancy, and for other purposes, also known as the Bankhead-Jones Farm Tenant Act. |
| 1937 | February 7 | A donated rope tow begins operation at Berthoud Pass, creating Colorado's first public tow-assisted alpine skiing. Unfortunately, two skiers are killed in an avalanche the same day. |
| 1937 | January 12 | Teller Ammons assumes office as the twenty-eighth Governor of the State of Colorado. |
| 1937 | January 3 | Ed Johnson takes his seat in the United States Senate. He will serve as a U.S. Senator from Colorado for 18 years. |
| 1937 | January 1 | Lieutenant Governor Ray Herbert Talbot assumes office as the twenty-seventh Governor of Colorado upon the resignation of Governor Ed Johnson to serve in the United States Senate. |
| 1936 | September 14 | The Town of Garden City incorporates. |
| 1936 | May 9 | Members of Civilian Conservation Corps (CCC) Company 1848 at Morrison Camp SP-13-C in Red Rocks Park cease work on all other projects in preparation for the construction of Red Rocks Amphitheatre. |
| 1935 | March 7 | The body of Elizabeth "Baby Doe" Tabor is found frozen to death in her cabin near the Matchless Mine in Lake County. |
| 1934 | May 17 | The Dotsero Cutoff of 38.1 miles (61.3 km) in Colorado reduces the Denver-Salt Lake City railroad route by 173 miles (278 km). |
| 1933 | March 2 | U.S. President Herbert Hoover issues a proclamation creating Black Canyon of the Gunnison National Monument. |
| 1933 | January 10 | Ed Johnson assumes office as the twenty-sixth Governor of the State of Colorado. |
| 1932 | March 28 | U.S. President Herbert Hoover issues an executive order creating Roosevelt National Forest. |
| 1932 | March 17 | U.S. President Herbert Hoover issues a proclamation creating Great Sand Dunes National Monument. |
| 1930 | April 1 | The 1930 United States census enumerates the population of the State of Colorado, later determined to be 1,035,791, an increase of 10.23% since the 1920 United States census. Colorado remains the 33rd most populous of the 48 U.S. states. |
| 1930 | January 22 | The Town of Bennett incorporates. |

### 1920s

| Year | Date | Event |
| 1929 | November | The City of Cañon City completes the Royal Gorge Bridge over the Arkansas River. |
| 1929 | October 17 | Denver Municipal Airport opens (renamed Stapleton Airfield in 1944, Stapleton International Airport in 1964). |
| 1929 | May 11 | U.S. President Herbert Hoover issues a proclamation creating Holy Cross National Monument. (Abolished August 3, 1950.) |
| 1928 | July 10 | The Town of Bethune incorporates. |
| 1928 | February 26 | The 6.2 mile (10.0 km) long Moffat Tunnel under the Continental Divide of the Americas opens as the world's longest railway tunnel. |
| 1927 | January 11 | Billy Adams assumes office as the twenty-fifth Governor of the State of Colorado. |
| 1926 | | Spencer Penrose establishes his Cheyenne Mountain Zoo near the BRO$^A$DMOOR. |
| 1925 | June | Adams State Normal School opens in Alamosa (named Adams State University in 2012). |
| 1925 | January 13 | Clarence Morley assumes office as the twenty-fourth Governor of the State of Colorado. |
| 1924 | June 2 | U.S. President Calvin Coolidge signs An Act To authorize the Secretary of the Interior to issue certificates of citizenship to Indians, also known as the Indian Citizenship Act of 1924, finally granting full United States Citizenship to all Native Americans born in the United States. |
| 1924 | March 11 | U.S. President Calvin Coolidge issues an executive order creating Grand Mesa National Forest. |
| 1923 | August 30 | The battleship USS Colorado (BB-45) is commissioned in New York Harbor. |
| 1923 | March 2 | U.S. President Warren G. Harding issues a proclamation creating Hovenweep National Monument. |
| 1923 | January 9 | William Ellery Sweet assumes office as the twenty-third Governor of the State of Colorado. |
| 1922 | March 10 | Denver radio station 9ZAF receives a commercial license as KLZ (AM 560 kHz), the first commercial radio station in Colorado. |
| 1921 | October 10 | The Town of Crowley incorporates. |
| 1921 | July 21 | The Colorado River designation is extended to its Grand River tributary, which has its source in Colorado. Grand River namesakes (e.g., valley, county, lake, and city) remain unchanged. |
| 1921 | June 3 | Flash floods on the Arkansas River and Fountain Creek kill 1500 people and inflict over $20 million of damage around Pueblo. |
| 1921 | March 26 | The Town of Branson incorporates. |
| 1920 | December 5 | Douglas Fairbanks becomes the first Coloradoan to star in a major motion picture: silent film The Mark of Zorro. |
| 1920 | July | The United States Army renames Army Hospital 21 in Aurora as Fitzsimons Army Hospital. |
| 1920 | June 15 | The Town of Eckley incorporates. |
| 1920 | April 1 | The 1920 United States census enumerates the population of the State of Colorado, later determined to be 939,629, an increase of 17.60% since the 1910 United States census. Colorado becomes the 33rd most populous of the 48 U.S. states. |
| 1920 | February 3 | The Town of Deer Trail incorporates. |

### 1910s

| Year | Date | Event |
| 1919 | December 19 | U.S. President Woodrow Wilson (guided by First Lady Ellen Axson Wilson) issues a proclamation creating Yucca House National Monument. |
| 1919 | October 2 | U.S. President Woodrow Wilson suffers a severe stroke after giving a speech in Pueblo. The stroke will leave the President incapacitated for the rest of his life. |
| 1919 | July 4 | Jack Dempsey of Manassa defeats Jess Willard in a bout at Toledo, Ohio for the World Heavyweight Boxing Championship. |
| 1919 | June 10 | The Town of Calhan incorporates. |
| 1918 | November 11 | An armistice halts the Great War. |
| 1918 | Autumn | The Denver Art Association becomes the Denver Art Museum. |
| 1918 | September 23 | The Town of Crook incorporates. |
| 1918 | August 29 | The Town of Arriba incorporates. |
| 1918 | June 29 | The Broadmoor resort opens near Colorado Springs at the site of the Broadmoor Casino and adjacent to the c. 1900 Broadmoor Shooting Grounds. |
| 1918 | May 14 | Denver Mayor Robert W. Speer dies at home in Denver at age 62. |
| 1918 | Spring | Construction of Army Hospital 21 begins in Aurora (named Fitzsimons Army Hospital in 1920, Fitzsimons Army Medical Center in 1974, closed 1999.) |
| 1917 | May 5 | The Town of Fleming incorporates. |
| 1917 | April 17 | The Town of Estes Park incorporates. |
| 1917 | April 17 | The Town of Cheraw incorporates. |
| 1917 | April 6 | The United States declares war on the German Empire and enters the Great War. |
| 1917 | January 10 | William Frederick "Buffalo Bill" Cody dies in Denver at age 70. |
| 1917 | January 9 | Julius Caldeen Gunter assumes office as the twenty-first Governor of the State of Colorado. |
| 1916 | November 2 | The Town of Flagler incorporates. |
| 1916 | August 25 | U.S. President Woodrow Wilson signs An Act To establish a National Park Service, and for other purposes. |
| 1916 | July 1 | Lieutenant Dwight D. Eisenhower marries Mamie Doud in Denver. |
| 1916 | January 29 | The Town of Eads incorporates. |
| 1916 | January 1 | State prohibition law comes into effect. |
| 1915 | October 4 | U.S. President Woodrow Wilson issues a proclamation creating Dinosaur National Monument. |
| 1915 | March 4 | Colorado creates its 3rd Congressional District and its 4th Congressional District to replace its two At-large Congressional seats. These two congressional districts remain to the present. |
| 1915 | January 26 | U.S. President Woodrow Wilson signs An Act to establish the Rocky Mountain National Park in the State of Colorado, and for other purposes. |
| 1915 | January 12 | George Alfred Carlson assumes office as the twentieth Governor of the State of Colorado. |
| 1914 | April 28-29 | The Battle of Walsenburg is fought between strikers and the Colorado National Guard as part of the violence stemming from the Ludlow Massacre and Colorado Coalfield War. |
| 1914 | April 20 | The Ludlow Massacre by the Colorado National Guard kills striking coal miners, 2 women, and 11 children. |
| 1913 | December 1 | Denver's greatest snowfall ever begins. Denver receives a five-day accumulation of 45.7 inches (1161 mm), while Georgetown gets 86 inches (2184 mm). |
| 1913 | March 8 | The State of Colorado creates Alamosa County from portions of Costilla and Conejos counties. |
| 1913 | January 14 | Elias M. Ammons assumes office as the nineteenth Governor of the State of Colorado. |
| 1912 | April 26 | The Colorado Mountain Club is founded in Denver. |
| 1912 | April 15 | The RMS Titanic strikes an iceberg and sinks. Margaret Brown of Denver is hailed as a heroine by survivors. |
| 1912 | March 18 | The Town of Gilcrest incorporates. |
| 1911 | November | The Daniels & Fisher Tower opens in Denver. |
| 1911 | July 17 | The Mountain States Telephone and Telegraph Company is formed in Denver. |
| 1911 | June 29 | U.S. President William Howard Taft issues a proclamation creating Durango National Forest. |
| 1911 | May 29 | The State of Colorado creates Crowley County from a portion of Otero County. |
| 1911 | May 24 | U.S. President William Howard Taft issues a proclamation creating Colorado National Monument. |
| 1911 | May 10 | Scottish operatic soprano Mary Garden sings in concert at the Park of the Red Rocks near Morrison. |
| 1911 | February 27 | The State of Colorado creates Moffat County from a portion of Routt County. |
| 1910 | December 19 | The Town of Crawford incorporates. |
| 1910 | July 1 | U.S. President William Howard Taft signs an executive order creating Colorado National Forest (renamed Roosevelt National Forest on March 28, 1932.) |
| 1910 | May 18 | The Town of Blanca incorporates. |
| 1910 | April 1 | The 1910 United States census enumerates the population of the State of Colorado, later determined to be 799,024, an increase of 48.05% since the 1900 United States census. Colorado becomes the 32nd most populous of the 46 U.S. states and will gain a 4th Congressional seat. |
| 1910 | February 15 | The Denver Public Library dedicates its new library building. |

### 1900s

| Year | Date | Event |
| 1909 | July 17 | The Shoshone Hydroelectric Generating Station begins transmitting electricity from Glenwood Canyon to the Denver area over the Shoshone Transmission Line. |
| 1909 | April 26 | U.S. President William Howard Taft issues executive orders creating Sopris National Forest. |
| 1909 | March 16 | U.S. President William Howard Taft issues executive orders creating La Sal National Forest. |
| 1909 | May 5 | The State of Colorado creates Jackson County from the western portion of Larimer County. |
| 1909 | March 4 | Edward T. Taylor takes his seat in the United States House of Representatives. Congressman Taylor will represent Colorado in the U.S. House for more than 32 years. |
| 1909 | January 19 | The Denver, Northwestern and Pacific Railway reaches Steamboat Springs. |
| 1909 | January 12 | John F. Shafroth assumes office as the eighteenth Governor of the State of Colorado. |
| 1908 | December 7 | U.S. President Theodore Roosevelt issues a proclamation creating Wheeler National Monument, the first Colorado National Monument. (Abolished August 3, 1950.) |
| 1908 | October 8 | The Town of Firestone incorporates. |
| 1908 | September 23 | The Town of Dacono incorporates. |
| 1908 | September 9 | The Town of Frederick incorporates. |
| 1908 | July 22 | The Town of Collbran incorporates. |
| 1908 | July 15 | The Town of Craig incorporates. |
| 1908 | July 10 | The Democratic National Convention meeting in Denver nominates William Jennings Bryan for President of the United States |
| 1908 | July 1 | U.S. President Theodore Roosevelt issues executive orders creating Rio Grande National Forest, Pike National Forest, Cochetopa National Forest, Arapaho National Forest, and Battlement National Forest. |
| 1908 | July 1 | The Colorado Museum of Natural History opens its new building in Denver City Park. |
| 1908 | June 25 | U.S. President Theodore Roosevelt issues executive orders creating Routt National Forest and Hayden National Forest. |
| 1907 | May 2 | The Town of Cedaredge incorporates. |
| 1907 | March 4 | The Town of Fletcher changes its name to the Town of Aurora. |
| 1907 | March 1 | U.S. President Theodore Roosevelt issues a proclamation creating the Las Animas Forest Reserve. |
| 1907 | February 2 | U.S. President Theodore Roosevelt issues a proclamation creating the Ouray Forest Reserve. |
| 1907 | January 18 | The Town of Center incorporates. |
| 1907 | January 8 | Henry Augustus Buchtel assumes office as the seventeenth Governor of the State of Colorado. |
| 1906 | August 18 | The Town of Bayfield incorporates. |
| 1906 | August 1 | The Argentine Central Railway reaches the 13,587-foot (4141 m) summit of Mount McClellan. |
| 1906 | June 29 | U.S. President Theodore Roosevelt signs An Act Creating the Mesa Verde National Park. |
| 1906 | June 8 | U.S. President Theodore Roosevelt signs An Act For the preservation of American antiquities, also known as the Antiquities Act of 1906, giving the President of the United States the authority to create national monuments on federal lands to protect significant natural, cultural, or scientific features. |
| 1906 | February 24 | U.S. President Theodore Roosevelt issues a proclamation creating the Fruita Forest Reserve. |
| 1906 | January 29 | The first Western Livestock Show opens in Denver. The show will become the National Western Stock Show, Rodeo and Horse Show. |
| 1906 | January 25 | U.S. President Theodore Roosevelt issues a proclamation creating the La Sal Forest Reserve. |
| 1905 | August 25 | U.S. President Theodore Roosevelt issues a proclamation creating the Holy Cross Forest Reserve. |
| 1905 | July 27 | The Town of Genoa incorporates. |
| 1905 | June 14 | U.S. President Theodore Roosevelt issues a proclamation creating the Uncompahgre Forest Reserve. |
| 1905 | June 13 | U.S. President Theodore Roosevelt issues proclamations creating the Cochetopa Forest Reserve and the Montezuma Forest Reserve. |
| 1905 | June 12 | U.S. President Theodore Roosevelt issues proclamations creating the Park Range Forest Reserve and the Wet Mountains Forest Reserve. |
| 1905 | June 3 | U.S. President Theodore Roosevelt issues a proclamation creating the San Juan Forest Reserve. |
| 1905 | May 12 | U.S. President Theodore Roosevelt issues proclamations creating the Gunnison Forest Reserve, the Leadville Forest Reserve, and the Pikes Peak Forest Reserve. |
| 1905 | May 9 | The first water flows over the spillway of the new Cheesman Dam on the South Platte River in Jefferson and Douglas counties. The dam is the world's tallest at 221 feet (67.3 m). |
| 1905 | April 5 | The Town of Eagle incorporates. |
| 1905 | March 17 | March 17 becomes Colorado's day with three governors as Alva Adams, James Hamilton Peabody, and Jesse Fuller McDonald sequentially serve as the Governor of the State of Colorado. |
| 1905 | January 19 | The armored cruiser USS Colorado (ACR-7) is commissioned at Philadelphia. |
| 1905 | January 10 | Alva Adams assumes office again as the fourteenth Governor of the State of Colorado. |
| 1904 | November 5 | The Town of Edgewater incorporates. |
| 1904 | August 24 | The Town of Arvada incorporates. |
| 1904 | June 1 | Robert W. Speer assumes office as the Mayor of the City and County of Denver. |
| 1904 | April 11 | The Town of Bergdorf incorporates. |
| 1903 | May 9 | The Town of Englewood incorporates. |
| 1903 | May 5 | The Town of Fletcher incorporates. Changes name to the Town of Aurora on March 4, 1907. |
| 1903 | April 23 | The Town of Fountain incorporates. |
| 1903 | April 11 | The State of Colorado changes the name of South Arapahoe County back to Arapahoe County. |
| 1903 | January 13 | James Hamilton Peabody assumes office as the thirteenth Governor of the State of Colorado. |
| 1902 | December 1 | The City and County of Denver begins operation and officially annexes the enclosed towns of Argo, Berkeley, Elyria, Globeville, Montclair, and Valverde. |
| 1902 | November 15 | After a prolonged court battle, the State of Colorado splits Arapahoe County into three new counties: the City and County of Denver, South Arapahoe County, and Adams County. |
| 1902 | November 10 | The Town of Cortez incorporates. |
| 1902 | July 18 | The Denver, Northwestern and Pacific Railway incorporates in Denver to construct a direct rail line to Salt Lake City via a tunnel under the Continental Divide. |
| 1902 | June 28 | U.S. President Theodore Roosevelt issues a proclamation creating the White River Forest Reserve. |
| 1902 | April 11 | U.S. President Theodore Roosevelt issues a proclamation creating the San Isabel Forest Reserve. |
| 1902 | January 24 | The Town of Crestone incorporates. |
| 1901 | August 26 | The Town of Basalt incorporates. |
| 1901 | January 8 | James Bradley Orman assumes office as the twelfth Governor of the State of Colorado. |
| 1900 | December 6 | The Colorado Museum of Natural History in Breckenridge is incorporated. |
| 1900 | August 25 | The Town of Fowler incorporates. |
| 1900 | July 19 | The Town of Dolores incorporates. |
| 1900 | April 1 | The 1900 United States census enumerates the population of the State of Colorado, later determined to be 539,700, an increase of 30.60% since the 1890 United States census. Colorado becomes the 31st most populous of the 45 U.S. states and will gain a 3rd Congressional seat. |

### 1890s

| Year | Date | Event |
| 1899 | June 1 | Nikola Tesla (Никола Тесла) begins research on the wireless transmission of power at his new laboratory in Colorado Springs. |
| 1899 | March 23 | The State of Colorado creates Teller County from portions of El Paso and Fremont counties. |
| 1899 | January 10 | Charles Spalding Thomas assumes office as the eleventh Governor of the State of Colorado. |
| 1898 | December 10 | The United States of America and the Kingdom of Spain sign the Treaty of Paris of 1898 to end the Spanish–American War. |
| 1898 | August 12 | The United States of America and the Kingdom of Spain sign a Protocol of Peace. |
| 1898 | April 23 | The Kingdom of Spain declares war on the United States of America. The United States declares war on Spain two days later. |
| 1898 | April 19 | U.S. Senator Henry M. Teller of Colorado offers the Teller Amendment to a Joint Resolution of Congress to ensure that the United States will not establish permanent control over Cuba after any conflict with Spain. |
| 1897 | June 23 | The City of Denver annexes the Town of Colfax. |
| 1897 | January 12 | Alva Adams assumes office again as the tenth Governor of the State of Colorado. |
| 1896 | November 7 | The Denver Zoo opens. |
| 1896 | September 6 | The City of Denver annexes the Town of Barnum. |
| 1896 | July 24 | The City of Denver annexes the Town of Highlands. |
| 1895 | November 15 | The Town of Del Norte incorporates. |
| 1895 | October 28 | Harry Heye Tammen and Frederick Gilmer Bonfils purchase the Evening Post of Denver for $12,500 (renamed Denver Evening Post November 3, The Denver Post January 1, 1901). |
| 1895 | February 20 | The City of Denver annexes the Town of Harman. |
| 1895 | January 8 | Albert McIntire assumes office as the ninth Governor of the State of Colorado. |
| 1894 | July 1 | The Florence and Cripple Creek Railroad reaches Cripple Creek. |
| 1894 | April 18 | The Town of Fruita incorporates. |
| 1894 | March 18 | Denver Union Station is extensively damaged by fire. |
| 1894 | March 14 | The Denver City Police and Arapahoe County Deputy Sheriffs barricade Denver City Hall to prevent the Colorado State Infantry from seizing the building in the City Hall War of 1894. |
| 1894 | February 7 | The City of Denver annexes the Town of South Denver. |
| 1894 | January 10 | The Town of Aguilar incorporates. |
| 1893 | November 7 | Colorado becomes the second U.S. state to grant women suffrage and the first state where the men voted to give women the right to vote. |
| 1893 | November 1 | U.S. President Grover Cleveland signs the Repeal of the Sherman Silver Purchase Act (enacted July 14, 1890), but the repeal fails to halt the Panic of 1893 and plunges Colorado into a massive economic depression. |
| 1893 | July 22 | Katharine Lee Bates visits the summit of Pikes Peak and writes the poem America the Beautiful. |
| 1893 | March 27 | The State of Colorado creates Mineral County from portions of Hinsdale, Rio Grande, and Saguache counties. |
| 1893 | January 10 | Davis Hanson Waite assumes office as the eighth Governor of the State of Colorado. |
| 1892 | December 24 | U.S. President Benjamin Harrison issues a proclamation creating the Battlement Mesa Forest Reserve. |
| 1892 | December 5 | The Town of Eaton incorporates. |
| 1892 | December 9 | U.S. President Benjamin Harrison issues a proclamation creating the South Platte Forest Reserve. |
| 1892 | August | Political supporters of Grover Cleveland found the Evening Post in Denver with $50,000. |
| 1892 | | Henry Perky of Denver develops a machine for making "little whole wheat mattresses", later called shredded wheat. |
| 1892 | June 23 | U.S. President Benjamin Harrison issues a proclamation creating the Plum Creek Timber Land Reserve. |
| 1892 | June 9 | The Town of Cripple Creek incorporates. |
| 1892 | May 19 | The Town of Creede incorporates. |
| 1892 | February 11 | U.S. President Benjamin Harrison issues a proclamation creating the Pikes Peak Timber Land Reserve. |
| 1891 | October 16 | The Denver and Rio Grande Railroad reaches Creede. |
| 1891 | October 16 | U.S. President Benjamin Harrison issues a proclamation creating the White River Plateau Timber Land Reserve, the second United States National Forest. |
| 1891 | July 1 | The Broadmoor Casino opens near Colorado Springs. |
| 1891 | March 3 | U.S. President Benjamin Harrison signs An act to repeal timber-culture laws, and for other purposes, also known as the Forest Reserve Act of 1891, giving the President of the United States the authority to create protected national forests on federal lands. |
| 1891 | January 13 | John Long Routt assumes office as the seventh Governor of the State of Colorado. |
| 1890 | October 22 | The Manitou and Pike's Peak Railway completes the rack and pinion line to the 14,115-foot (4,302 m) summit of Pikes Peak. |
| 1890 | October 20 | Rancher Robert Miller Womack discovers a rich gold lode along Cripple Creek near Pikes Peak. The Cripple Creek Mining District will produce more than 730 tonnes of gold, the most of any Rocky Mountain district. |
| 1890 | October 9 | The Town of Elizabeth incorporates. |
| 1890 | July 4 | The Colorado State Capitol cornerstone is placed for the new building on Brown's Bluff in Denver. |
| 1890 | May 14 | The Town of Cheyenne Wells incorporates. |
| 1890 | April 1 | The 1890 United States census enumerates the population of the State of Colorado, later determined to be 413,249, an increase of 112.66% since the 1880 United States census. Colorado becomes the 31st most populous of the 44 U.S. states and will gain a 2nd Congressional District. |
| 1890 | January 18 | The Town of De Beque incorporates. |
| 1890 | January 15 | The Town of Fort Lupton incorporates. |

### 1880s

| Year | Date | Event |
| 1889 | December 29 | The Town of Antonito incorporates. |
| 1889 | June 24 | The Denver and Rio Grande Railroad reaches Lake City. |
| 1889 | June | The City of Denver establishes the Denver Public Library. |
| 1889 | April 16 | The State of Colorado creates Baca County from a portion of Las Animas County, and Montezuma County from a portion of La Plata County. |
| 1889 | April 11 | The State of Colorado creates Kiowa, Kit Carson, Lincoln, and Prowers counties from portions of Bent and Elbert counties. |
| 1889 | April 9 | The State of Colorado creates Sedgwick County from a portion of Logan County. |
| 1889 | March 27 | The State of Colorado creates Phillips County from a portion of Logan County. |
| 1889 | March 25 | The State of Colorado creates Cheyenne County from portions of Elbert and Bent counties, Otero County from a portion of Bent County, and Rio Blanco County from a portion of Garfield County. |
| 1889 | March 15 | The State of Colorado creates Yuma County from a portion of Washington County. |
| 1889 | February 19 | The State of Colorado creates Morgan County from a portion of Weld County. |
| 1889 | January 8 | Job Adams Cooper assumes office as the sixth Governor of the State of Colorado. |
| 1888 | December 18 | Richard Wetherill and Charlie Mason find the Cliff Palace on Mesa Verde. |
| 1888 | August 28 | The Town of Berthoud incorporates. |
| 1888 | April 26 | The Town of Carbondale incorporates. |
| 1888 | April 9 | The Denver, Texas and Fort Worth Railroad begins service between Denver and Fort Worth. |
| 1888 | January 12 | The Town of Burlington incorporates. |
| 1888 | January 1 | The Missouri Pacific Railroad begins service between Pueblo, Kansas City, and Saint Louis. |
| 1887 | November 8 | John Henry "Doc" Holliday, dentist, gambler, and gunfighter, dies of tuberculosis in Glenwood Springs at age 36. |
| 1887 | November 5 | The Atchison, Topeka and Santa Fe Railroad reaches Denver. |
| 1887 | October 31 | The United States Army establishes Fort Logan southwest of Denver (transferred from the Army Air Service Command to the Veterans Administration in May 1946.) |
| 1887 | October 28 | The Denver and Rio Grande Railroad reaches Aspen. |
| 1887 | October 6 | The Denver and Rio Grande Railroad reaches Glenwood Springs via Glenwood Canyon. |
| 1887 | September 22 | The Town of Akron incorporates. |
| 1887 | September 13 | The Town of Florence incorporates. |
| 1887 | September 3 | The Colorado Midland Railroad begins service between Colorado City and Leadville via Buena Vista and Hagerman Tunnel under the Continental Divide of the Americas. |
| 1887 | September 1 | The Town of Brighton incorporates. |
| 1887 | June 15 | The Town of Fort Morgan incorporates. |
| 1887 | February 25 | The State of Colorado creates Logan County from a portion of Weld County. |
| 1887 | February 9 | The State of Colorado creates Washington County from a portion of Weld County. |
| 1887 | January 11 | Alva Adams assumes office as the fifth Governor of the State of Colorado. |
| 1886 | July 12 | The City of Blackhawk incorporates. |
| 1886 | June 19 | The Town of Colorado Springs incorporates. Colorado Springs is the seat of El Paso County. |
| 1886 | June 12 | The City of Central incorporates. Central City is the seat of Gilpin County. |
| 1885 | November 15 | The Town of Silverton incorporates. Silverton is the seat of San Juan County. |
| 1885 | November 15 | The Town of Pueblo incorporates. Pueblo is the seat of Pueblo County. |
| 1885 | November 15 | The Town of Greeley incorporates. Greeley is the seat of Weld County. |
| 1885 | November 15 | The Town of Evans incorporates. |
| 1885 | November 15 | The Town of Erie incorporates. |
| 1885 | April 14 | The State of Colorado creates Archuleta County from a portion of Conejos County. |
| 1885 | January 13 | Benjamin Harrison Eaton assumes office as the fourth Governor of the State of Colorado. |
| 1884 | November 24 | The Town of Brush incorporates. |
| 1884 | April | The Georgetown, Breckenridge and Leadville Railway reaches SilverPlume via the Georgetown Loop. |
| 1883 | March 2 | The State of Colorado creates San Miguel County from a portion of San Juan County, and reverts the name of Uncompahgre County back to Ouray County. |
| 1883 | March 1 | U.S. Senator Horace Tabor of Colorado marries Elizabeth "Baby Doe" McCourt in Washington, D.C. |
| 1883 | February 27 | The Colorado General Assembly renames Ouray County as Uncompahgre County. |
| 1883 | February 14 | The State of Colorado creates Mesa County from a portion of Gunnison County. |
| 1883 | February 12 | The Town of Fort Collins incorporates. Fort Collins is the seat of Larimer County. |
| 1883 | February 11 | The State of Colorado creates Eagle County from a portion of Summit County, and Delta and Montrose counties from portions of Gunnison County. |
| 1883 | February 10 | The State of Colorado creates Garfield County from a portion of Summit County. |
| 1883 | January 26 | The Town of Dillon incorporates. |
| 1883 | January 9 | James Benton Grant assumes office as the third Governor of the State of Colorado. |
| 1882 | December 19 | The Denver and Rio Grande Railroad reaches the Colorado-Utah Territory border west of Grand Junction. |
| 1882 | November 21 | The Denver and Rio Grande Railroad reaches Grand Junction. |
| 1882 | November 7 | An earthquake estimated at 6.2 M$_{fa}$ affects the Denver area with a maximum Mercalli intensity of VII (Very strong). The quake causes minor damage in Colorado and southern Wyoming and is the most intense in Colorado recorded history. |
| 1882 | October 24 | The Town of Delta incorporates. |
| 1882 | September 8 | The Denver and Rio Grande Railroad reaches Montrose. |
| 1882 | September 6 | The Denver, South Park and Pacific Railroad reaches Gunnison via the Alpine Tunnel under the Continental Divide of the Americas. |
| 1882 | July 8 | The Denver and Rio Grande Railroad reaches Silverton. |
| 1882 | June 26 | The Chicago, Burlington and Quincy Railroad reaches Denver. |
| 1882 | May 7 | The Denver and New Orleans Railroad begins service between Denver and Pueblo. |
| 1882 | May 6 | U.S. President Chester A. Arthur signs the Chinese Exclusion Act banning Chinese immigration to the United States and denying citizenship to all persons of Chinese ancestry. |
| 1882 | April 18 | U.S. President Chester A. Arthur appoints Henry Moore Teller as U.S. Secretary of the Interior. Teller is the first Coloradan to serve in the Cabinet of the United States.. |
| 1882 | April 13 | Oscar Wilde visits Leadville and later writes, "They afterwards took me to a dancing saloon where I saw the only rational method of art criticism I have ever come across. Over the piano was printed a notice : — PLEASE DO NOT SHOOT THE PIANIST. HE IS DOING HIS BEST." |
| 1882 | April 12 | The Town of Empire incorporates. |
| 1882 | February 11 | The Town of Coal Creek incorporates. |
| 1881 | November 24 | The Denver and Rio Grande Railroad reaches Crested Butte. |
| 1881 | November 8 | The City of Denver is made the permanent capital of the State of Colorado by a state referendum. |
| 1881 | August 8 | The Denver and Rio Grande Railroad reaches Gunnison. |
| 1881 | July 27 | The Denver and Rio Grande Railroad reaches Durango. |
| 1881 | June 1 | Denver Union Station opens. |
| 1881 | May 17 | The Town of Castle Rock incorporates. |
| 1881 | April 27 | The Town of Durango incorporates. |
| 1881 | April 1 | The Town of Aspen incorporates. |
| 1881 | March 4 | The State of Colorado creates Dolores County from a portion of Ouray County. |
| 1881 | February 23 | The State of Colorado creates Pitkin County from a portion of Gunnison County. |
| 1881 | February 21 | The Colorado Electric Company incorporates in Denver. |
| 1881 | January 13 | The Town of Bonanza City incorporates. |
| 1880 | December 3 | The Town of Frisco incorporates. |
| 1880 | July 22 | The Denver and Rio Grande Railroad reaches Leadville. The first passenger train to Leadville carries former President Ulysses Grant, the man who brought Colorado statehood. |
| 1880 | July 15 | The Town of Crested Butte incorporates. |
| 1880 | June 1 | The Denver and Rio Grande Railroad reaches the Colorado-New Mexico Territory border south of Antonito. |
| 1880 | April 1 | The 1880 United States census enumerates the population of the State of Colorado, later determined to be 194,327, an increase of 387% since the 1870 United States census. Colorado becomes the 35th most populous of the 38 U.S. states. |
| 1880 | March 27 | The Denver and Rio Grande Railway reaches a legal accommodation with the Atchison, Topeka and Santa Fe Railroad known as the Treaty of Boston. |
| 1880 | March 3 | The Denver, South Park and Pacific Railroad reaches Buena Vista. |
| 1880 | March 3 | The Town of Breckenridge incorporates. |

### 1870s

| Year | Date | Event |
| 1879 | November 8 | The Town of Buena Vista incorporates. |
| 1879 | September 1 | Colorado Agricultural College opens to students. The land-grant college is renamed Colorado State College of Agriculture and Mechanic Arts in 1935, and renamed Colorado State University in 1957. |
| 1879 | July | The Colorado Historical Society is founded in Denver. |
| 1879 | May 7 | The first passenger train passes through the Royal Gorge. |
| 1879 | April 21 | The United States Supreme Court rules in the Royal Gorge War between the Denver and Rio Grande Railway and the Atchison, Topeka, and Santa Fe Railroad. |
| 1879 | February 24 | The Denver Telephone Dispatch Company opens for business. |
| 1879 | February 10 | The Colorado General Assembly abolishes Carbonate County after two days and splits its territory between a new Chaffee County and a renamed Lake County. |
| 1879 | February 8 | The Colorado General Assembly renames Lake County as Carbonate County. |
| 1879 | January 14 | Frederick Walker Pitkin assumes office as the second Governor of the State of Colorado. |
| 1878 | December 7 | The Atchison, Topeka and Santa Fe Railroad reaches Raton Pass on the Santa Fe Trail, blocking the Denver and Rio Grande Railway's route to Santa Fe. |
| 1878 | August 12 | The Town of Alamosa incorporates. |
| 1878 | June 26 | The Denver and Rio Grande Railway reaches Alamosa. |
| 1878 | April 19 | The Royal Gorge War begins as a construction crew of the Atchison, Topeka and Santa Fe Railroad blocks a crew of the Denver and Rio Grande Railway from building into the Royal Gorge. |
| 1878 | May 22 | The Colorado Central Railroad reaches Central City. |
| 1878 | January 1 | David May opens The Great Western Auction House and Clothing Store in Leadville. |
| 1877 | September 16 | The Solid Muldoon is uncovered on Muldoon Hill near Beulah. |
| 1877 | September | David May, Jacob Holcombe, and Thomas Dean open a dry goods store in Leadville. The store will become the first component of The May Department Stores Company. |
| 1877 | August 13 | The Colorado Central Railroad reaches Georgetown. |
| 1877 | March 9 | The State of Colorado creates Custer County from a portion of Fremont County, and Gunnison County from a portion of Lake County. |
| 1877 | January 29 | The State of Colorado creates Routt County from a portion of Grand County. |
| 1877 | January 18 | The State of Colorado creates Ouray County from portions of Hinsdale and Lake counties. |
| 1876 | November 1 | The Colorado General Assembly convenes for the first time. |
| 1876 | October 3 | Voters of the new State of Colorado elect Territorial Governor John Long Routt as their first State Governor, Henry Moore Teller and Jerome Bunty Chaffee as their first U.S. Senators, and James Burns Belford as their first U.S. Representative. |
| 1876 | August 1 | U.S. President Ulysses S. Grant certifies that the conditions of the Colorado Enabling Act have been fulfilled and issues Proclamation 230 — Admission of Colorado into the Union. The Territory of Colorado becomes the State of Colorado, the 38th U.S. state. |
| 1876 | July 4 | The Territory of Colorado celebrates the Centennial of the United States of America while still reeling from the defeat of Lieutenant Colonel George Armstrong Custer and the 7th Cavalry Regiment at the Battle of the Little Bighorn on June 26. |
| 1876 | July 1 | Voters of the Territory of Colorado approve the proposed Constitution of the State of Colorado by a vote of 15,443 to 4,039. |
| 1876 | March 14 | The Colorado Constitutional Convention adopts the proposed Constitution of the State of Colorado |
| 1876 | March 14 | The Territory of Colorado establishes the University of Colorado at Boulder. |
| 1876 | February 29 | The Atchison, Topeka and Santa Fe Railroad reaches Pueblo. |
| 1876 | January 31 | The Territory of Colorado creates San Juan County from a portion of Lake County. |
| 1875 | October 25 | The Colorado Constitutional Convention convenes in Denver to write a state constitution. |
| 1875 | October 5 | Ulysses S. Grant becomes the first President of the United States to visit the Colorado Territory. |
| 1875 | March 29 | U.S. President Ulysses S. Grant appoints John Long Routt to be the eighth (and last) Governor of the Territory of Colorado. |
| 1875 | March 3 | U.S. President Ulysses S. Grant signs An Act to enable the people of Colorado to form a constitution and State government, and for the admission of the said State into the Union on an equal footing with the original States. |
| 1875 | March 3 | U.S. President Ulysses S. Grant signs the Page Act limiting the immigration of Asians into the United States. |
| 1874 | August 14 | Members of the Wheeler Survey make the first recorded ascent of Blanca Peak in the San Luis Valley. |
| 1874 | July 6 | The Denver and Rio Grande Railway reaches Cañon City. |
| 1874 | June 19 | U.S. President Ulysses S. Grant appoints Edward M. McCook a second time to be the seventh Governor of the Territory of Colorado. |
| 1874 | February 10 | The Territory of Colorado creates Hinsdale, La Plata, and Rio Grande counties from portions of Conejos, Costilla, and Lake counties. |
| 1874 | February 9 | The Territory of Colorado purchases the Territorial School of Mines in Golden from the Episcopal Church for $5,000. |
| 1874 | February 9 | The Territory of Colorado abolishes Platte County after organizers fail to secure voter approval. The territory of the county is returned to Weld County. |
| 1874 | February 6 | The Territory of Colorado abolishes Greenwood County and divides its territory between Elbert County and Bent County. |
| 1874 | February 3 | The Territory of Colorado creates Elbert County from a portion of Douglas County, and Grand County from a portion of Summit County. |
| 1873 | December 2 | The Town of Alma incorporates. |
| 1873 | September 17 | The Denver and Boulder Valley Railroad reaches Boulder. |
| 1873 | June 16 | The Town of Walsenburg incorporates. Walsenburg is the seat of Huerfano County. |
| 1873 | April 4 | U.S. President Ulysses S. Grant appoints Samuel Hitt Elbert to be the sixth Governor of the Territory of Colorado. |
| 1872 | December 15 | The Colorado Central Railroad reaches Black Hawk. |
| 1872 | November 15 | The Town of Fairplay incorporates. Fairplay is the seat of Park County. |
| 1872 | October 9 | The first Southern Colorado Agricultural and Industrial Exposition is held in Pueblo. The exposition will become the Colorado State Fair. |
| 1872 | October 2 | The Denver, South Park and Pacific Railroad incorporates in Denver to build a narrow gauge railway through South Park to the Gunnison River and the Utah Territory. |
| 1872 | June 15 | The Denver and Rio Grande Railway reaches Pueblo. |
| 1872 | April 3 | The Town of Cañon City incorporates. Cañon City (also spelled Canyon City and Canon City) is the seat of Fremont County. |
| 1872 | February 11 | The Territory of Colorado creates Platte County from the eastern portion of Weld County. |
| 1871 | November 4 | The City of Boulder incorporates. Boulder City is the seat of Boulder County. |
| 1871 | October 27 | The Denver and Rio Grande Railway is completed from Denver to the new town of Colorado Springs, bypassing Colorado City 5 mi (8.0 km) to the west. |
| 1871 | January 2 | The City of Golden incorporates. Golden City is the former territorial capital and the seat of Jefferson County. |
| 1870 | October 27 | The Denver and Rio Grande Railway incorporates in Denver. The company plans to build a narrow gauge railway from Denver south to Santa Fe, New Mexico Territory; El Paso, Texas; and on to Mexico City. |
| 1870 | September 22 | The Colorado Central Railroad reaches Golden from Denver. |
| 1870 | August 15 | The Kansas Pacific Railroad reaches Denver from Kansas City, Missouri, creating the first all-rail transcontinental route. |
| 1870 | June 21 | The Denver Pacific Railroad reaches Denver from the Union Pacific mainline at Cheyenne, Wyoming Territory. |
| 1870 | May 2 | Episcopal Bishop George Maxwell Randall begins construction of the Territorial School of Mines at Golden City. |
| 1870 | April 1 | The 1870 United States census enumerates the population of the Territory of Colorado, later determined to be 39,864, an increase of 16% since the 1860 United States census. Colorado becomes the 3rd most populous of the nine U.S. territories. |
| 1870 | February 11 | The Territory of Colorado creates Bent and Greenwood counties from expropriated Cheyenne and Arapaho tribal land and portions of Huerfano County. |

### 1860s

| Year | Date | Event |
| 1869 | December 14 | Nathan Meeker, agricultural editor of the New York Tribune, appeals to readers of high moral character to help him build a utopian farming community between the Cache La Poudre River and the South Platte River in the Territory of Colorado. Meeker will name the community Greeley in honor of his publisher, Horace Greeley. |
| 1869 | November 13 | The Denver Gas Company incorporates in Denver. |
| 1869 | August 19 | S.F. Sharpless and William M. Davis make the first recorded ascent of Mount Harvard, highest of the Collegiate Peaks. |
| 1869 | July 11 | The Battle of Summit Springs, an armed conflict between the United States Army and a group of Cheyenne Dog Soldiers, takes place in Washington County. |
| 1869 | July 4 | Deer Trail hosts the world's first organized rodeo. |
| 1869 | | Surveyor O.N. Chaffee determines the eastern boundary of the Colorado Territory beginning from Julesburg. |
| 1869 | June 14 | U.S. President Ulysses S. Grant appoints Edward M. McCook to be the fifth Governor of the Territory of Colorado. |
| 1869 | March 4 | Commanding General of the United States Army Ulysses S. Grant assumes office as the 18th President of the United States. |
| 1868 | August 23 | A party led by John Wesley Powell makes the first recorded (White) ascent of Longs Peak. |
| 1868 | July 9 | The Fourteenth Amendment to the United States Constitution is ratified. |
| 1868 | May 23 | Brigadier General Kit Carson dies at new Fort Lyon at age 58. |
| 1868 | January 10 | The Territory of Colorado incorporates the Town of Georgetown. The Town of Georgetown is the only Colorado municipality still operating under its original charter from the Territory of Colorado. |
| 1867 | December 9 | The Colorado General Assembly votes to move the territorial capital from Golden City to Denver, the seat of Arapahoe County. |
| 1867 | November 18 | The Union Pacific Railroad reaches Julesburg and eventually will have 9 miles (14 km) of mainline in the Colorado Territory. |
| 1867 | April 24 | U.S. President Andrew Johnson appoints Alexander Cameron Hunt to be the fourth Governor of the Territory of Colorado. |
| 1866 | December 29 | The Colorado General Assembly creates Saguache County from portions of Lake and Costilla counties. |
| 1866 | March 6 | Brigadier General Kit Carson takes command of Fort Garland in the San Luis Valley in an effort to make peace with the Ute Nation. |
| 1866 | February 13 | The City of Denver City shortens its name to the City of Denver. |
| 1866 | February 9 | The Colorado General Assembly creates Las Animas County from a portion of Huerfano County. |
| 1865 | October 17 | U.S. President Andrew Johnson appoints Alexander Cummings of Pennsylvania to be the third Governor of the Territory of Colorado. |
| 1865 | September | The (White male) voters of the Territory defeat a referendum for universal male suffrage by a vote of 476 to 4,192, denying the vote to Indians, Negros, Asians, as well as women. |
| 1865 | August 1 | John Evans resigns as Governor of the Territory of Colorado. There will be no territorial governor until October 17, 1865. |
| 1865 | July 18 | U.S. President Andrew Johnson demands that John Evans resign as the Governor of the Territory of Colorado following an investigation of the Sand Creek Massacre. |
| 1865 | May 9 | U.S. President Andrew Johnson proclaims the end of the American Civil War. |
| 1865 | April 15 | U.S. Vice President Andrew Johnson assumes office as the 17th President of the United States upon the assassination of Abraham Lincoln. |
| 1865 | January 7 | The Battle of Julesburg, a skirmish between one thousand Cheyenne, Arapaho, and Lakota Indians and about sixty U.S. army soldiers along with forty to fifty civilians, takes place at Julesburg.. |
| 1864 | November 29 | Colonel (and the Reverend) John Chivington orders the murder of hundreds of Cheyenne and Arapaho people in the Sand Creek Massacre. |
| 1864 | October 22 | The Union Army moves Camp Collins downstream to the present site of Fort Collins. |
| 1864 | June 11 | Near Elizabeth in Elbert County, Nathan Hungate, his wife, and his two daughters are murdered, presumably by American Indians, in the Hungate massacre. Public anger following the killings later leads to the Sand Creek massacre. |
| 1864 | May 19 | A flash flood on Cherry Creek sweeps away many low-lying structures of Denver City and separates many residents from their local saloons and brothels. |
| 1864 | March 3 | Governor John Evans and the Reverend John Chivington found Colorado Seminary in Denver City. The seminary will close in 1868, but reopen in 1880 as the University of Denver. |
| 1863 | January 2 | The Boonville post office opens. |
| 1862 | December 6 | The Black Hawk Point post office opens. |
| 1862 | August 14 | The Colorado General Assembly votes to move the territorial capital from Colorado City to Golden City, the seat of Jefferson County. |
| 1862 | July 22 | The Union Army establishes Camp Collins near Colona. |
| 1862 | July 11 | Unable to find adequate accommodations in Colorado City, the Colorado General Assembly votes to adjourn and reconvene in Denver City on July 16. |
| 1862 | July 7 | The second session of the Colorado General Assembly convenes in Colorado City. |
| 1862 | April 6 | Alferd Packer arrives at the Los Pinos Indian Agency in the Cochetopa Hills with no trace of his five companions. Upon questioning, Packer admits that he ate his companions. |
| 1862 | March 28 | Colorado volunteers under the command of Colonel John P. Slough repulse Texas cavalry under the command of Lieutenant Colonel William Read Scurry at the Battle of Glorieta Pass. The battle effectively ends the Confederate New Mexico Campaign. |
| 1862 | March 26 | U.S. President Abraham Lincoln appoints John Evans of Illinois to be the second Governor of the Territory of Colorado. |
| 1862 | March 10 | Texas cavalry under the command of Brigadier General Henry Hopkins Sibley occupy Santa Fe in the Confederate New Mexico Campaign. |
| 1862 | February 9 | Alferd Packer and five companions leave the camp of Ouray on the Uncompahgre River bound for the Cochetopa Hills. |
| 1861 | November 7 | The Colorado General Assembly reincorporates the City of Denver, Auraria, and Highland as the City of Denver (still commonly known as Denver City), the seat of Arapahoe County. |
| 1861 | November 7 | The Colorado General Assembly renames Guadaloupe County as Conejos County after only six days. |
| 1861 | November 5 | The Colorado General Assembly votes to move the territorial capital from Denver City to Colorado City, the seat of El Paso County. |
| 1861 | November 1 | The Colorado General Assembly creates 17 original counties: Arapahoe, Boulder, Clear Creek, Costilla, Douglas, El Paso, Fremont, Gilpin, Guadaloupe, Huerfano, Jefferson, Lake, Larimer, Park, Pueblo, Summit, and Weld County. |
| 1861 | September 9 | The first session of Colorado General Assembly convenes in Denver City. The legislature reenacts many of the laws of the Provisional Government of the Territory of Jefferson. |
| 1861 | June 6 | Jefferson Territorial Governor Robert Williamson Steele proclaims the Territory of Jefferson officially disbanded after meeting with Colorado Territorial Governor William Gilpin. |
| 1861 | May 27 | Governor William Gilpin arrives in Denver City. |
| 1861 | April 12 | The American Civil War begins with the Battle of Fort Sumter. |
| 1861 | March 25 | U.S. President Abraham Lincoln appoints William Gilpin of Missouri to be the first Governor of the Territory of Colorado. |
| 1861 | March 4 | Abraham Lincoln assumes office as the 16th President of the United States. |
| 1861 | February 28 | U.S. President James Buchanan signs An Act to provide a temporary Government for the Territory of Colorado, creating the free Territory of Colorado. The new territory is created from the unorganized territory previously part of the Territory of Kansas, the northern portion of the Territory of New Mexico, the eastern portion of the Territory of Utah, and the southwestern portion of the Territory of Nebraska. The new name is chosen because the Colorado River is thought to originate somewhere in the Territory. The new territory is 41% smaller than the provisional Territory of Jefferson. The boundaries of the Colorado Territory are essentially the same as the present State of Colorado. |
| 1861 | February 8 | Seven secessionist slave states create the Confederate States of America. |
| 1861 | January 29 | U.S. President James Buchanan signs An Act for the Admission of Kansas into the Union, creating the free State of Kansas from the eastern portion of the Territory of Kansas. The western portion of the Kansas Territory becomes unorganized territory, although the Provisional Government of the Territory of Jefferson continues to act as the de facto government. |
| 1860 | November 13 | The Jefferson General Assembly moves from Denver City to Golden City, the new seat of Jefferson County. |
| 1860 | November 6 | Abraham Lincoln is elected President of the United States. Seven slave states will secede from the United States of America before February 8, 1861. |
| 1860 | August 7 | A proclamation by Territorial Governor Steele proposes a merger of the Jefferson Territory with the Kansas Territory. Bleeding Kansas rejects the proposal outright. |
| 1860 | April 1 | The 1860 United States census enumerates the population of the Pike's Peak Country, later determined to be 34,277. Most of the miners in the backcountry prospecting for gold could not be counted, so there may have been a substantial undercount. |
| 1860 | February 1 | The Territory of New Mexico creates Mora County from parts of Taos County and San Miguel County. The new county extends into the southern portion of the Jefferson Territory and the future State of Colorado. |
| 1860 | January 23 | The second session of the Jefferson General Assembly convenes in Denver City, the seat of Arrappahoe County. |
| 1860 | January 1 | At the behest of the Jefferson General Assembly, Samuel Beall requests that the U.S. Congress approve the new Territory of Jefferson. Congress does not respond. |

### 1850s

| Year | Date | Event |
| 1859 | December | Frederick Salomon opens the Rocky Mountain Brewery in Denver City, the first brewery in the Jefferson Territory. |
| 1859 | December 3 | The Jefferson General Assembly grants a charter to the consolidated City of Denver, Auraria, and Highland, more commonly known as Denver City, as the territorial capital and seat of Arrappahoe County. |
| 1859 | November 28 | The Jefferson General Assembly creates 12 counties: Arrappahoe, Cheyenne, El Paso, Fountain, Heele, Jackson, Jefferson, Mountain, North, Park, St. Vrain, and Saratoga County. |
| 1859 | November 7 | The first session of the Jefferson General Assembly convenes in Denver City. |
| 1859 | October 24 | Voters of the Pike's Peak Country approve the establishment of the Provisional Government of the Territory of Jefferson by a vote of 1,852 to 280 and elect Robert Williamson Steele the first (and only) Governor of the Territory of Jefferson. The Jefferson Territory extended from the 102nd meridian west to the 110th meridian west and from the 37th parallel north to the 43rd parallel north, and encompassed all of the present U.S. state of Colorado and portions of Utah, Wyoming, Nebraska, and Kansas. The Jefferson Territory served as the de facto government of the region until Governor Steele proclaimed the government disbanded on June 6, 1861. |
| 1859 | September 24 | Voters of the Pike's Peak Country reject the proposal to create a Provisional State of Jefferson. |
| 1859 | June 16 | Golden City is established 13 miles (21 km) west of Denver City in northwestern Kansas Territory. |
| 1859 | May 7 | The first stagecoach arrives in Denver City from Leavenworth, Kansas Territory. |
| 1859 | May 6 | John H. Gregory discovers the first hard rock gold in the Rocky Mountains, a rich gold-bearing vein at Gregory Gulch, 28 miles (45 km) west of Denver City. |
| 1859 | April 23 | William Byers publishes the first edition of the Rocky Mountain News, the Rocky Mountain region's first newspaper, at Auraria. |
| 1859 | April 22 | The Boulder, Nebraska Territory post office opens. |
| 1859 | April 15 | Ten delegates from six communities in the Pike's Peak Country meet in convention at Dick Wooton's store in Auraria to pass resolutions to organize a proposed Provisional State of Jefferson. |
| 1859 | February 7 | The Territory of Kansas splits Arapahoe County into the six counties of Arapahoe, Broderick, El Paso, Fremont, Montana, and Oro, and creates the new Peketon County farther east and south. The counties are never organized. |
| 1859 | January 18 | The Auraria, Kansas Territory post office opens. |
| 1859 | January 18 | The Saint Vrain, Nebraska Territory post office opens. |
| 1858 | November 22 | A group of Kansas Territory speculators led by William Larimer organize the rival townsite of Denver City across Cherry Creek from Auraria on the property of the St. Charles Town Company. |
| 1858 | October 29 | Charles H. Blake and A.J. Williams open a mercantile business out of wagons in Auraria. |
| 1858 | October 3 | A group of Georgia prospectors led by Green Russell establish the townsite of Auraria south of Cherry Creek near the Cherry Creek Diggings. |
| 1858 | September 24 | Prospectors from Montana City organize the St. Charles Town Company east of the Cherry Creek Diggings in Arapahoe County, Kansas Territory. |
| 1858 | August 26 | Gold dust from the Little Dry Creek Diggings arrives in Kansas City, precipitating the Pike's Peak Gold Rush. |
| 1858 | August | Prospectors from Lawrence, Kansas Territory establish the townsite of Montana City one mile (1.6 km) north of the Little Dry Creek Diggings in Arapahoe County, Kansas Territory. |
| 1858 | July | Georgia prospectors Green Russell and Sam Bates discover a placer deposit yielding about 20 troy ounces (622 grams) of gold near the mouth of Little Dry Creek in Arapahoe County, Kansas Territory. |
| 1858 | spring | Antoine Janis establishes the town of Colona on the Cache la Poudre River in western Nebraska Territory. |
| 1858 | spring | The U.S. Army builds Fort Garland in the San Luis Valley to replace Fort Massachusetts six miles to the north. |
| 1857 | summer | A party of Mexican-American prospectors from Taos County, New Mexico Territory dig for gold along the South Platte River below the mouth of Little Dry Creek in Arapahoe County, Kansas Territory. |
| 1856 | January 5 | The Territory of Utah creates Beaver County from a part of Iron County which extends into the future State of Colorado. |
| 1855 | August 25 | The Territory of Kansas creates Arapahoe County in the extreme western portion of the territory in what is now Colorado. Despite several attempts, the county is never organized. |
| 1854 | May 30 | U.S. President Franklin Pierce signs An Act to Organize the Territories of Nebraska and Kansas. This act supersedes the Missouri Compromise and provides for the voters of the territories to decide for themselves whether to permit slavery. The Territory of Kansas includes all of the future State of Colorado east of the Continental Divide and south of the 40th parallel north (the Baseline). The Territory of Nebraska includes all of the future State of Colorado east of the Continental Divide and north of the 40th parallel north. The Kansas–Nebraska Act will unwittingly lead to the American Civil War. |
| 1852 | June 22 | The U.S. Army establishes Fort Massachusetts in the San Luis Valley of northern New Mexico Territory, the first U.S. Army fort in the future State of Colorado. |
| 1852 | March 3 | The new Territory of Utah creates ten counties, including Great Salt Lake, Green River, Iron, Sanpete, Utah, and Washington counties which extend into the future State of Colorado. |
| 1852 | January 9 | The new Territory of New Mexico creates nine original counties, including Taos County which extends into the future State of Colorado. |
| 1851 | April 9 | The first permanent European-American settlement in the future State of Colorado is established at San Luis de la Culebra in the northern New Mexico Territory by settlers from the Taos area. |
| 1851 | April 4 | The General Assembly of the State of Deseret dissolves the provisional government and yields to the Territory of Utah. |
| 1850 | September 9 | The Territory of New Mexico and the Territory of Utah are established as part of the Compromise of 1850. U.S. President Millard Fillmore signs An Act proposing to the State of Texas the Establishment of her Northern and Western Boundaries, the Relinquishment by the said State of all Territory claimed by her exterior to said Boundaries, and of all her Claims upon the United States, and to establish a territorial Government for New Mexico. The Territory of New Mexico includes the southeastern portion of the future State of Colorado lying south of the 38th parallel north and east of the Continental Divide. President Fillmore also signs An Act to establish a Territorial Government for Utah. The Territory of Utah includes all of the future State of Colorado lying west of the Continental Divide. |
| 1850 | June 22 | Georgia prospector Lewis Ralston pans about a quarter of a troy ounce (8 grams) of gold near the mouth of a creek (later named Ralston Creek) in northwestern Kansas Territory, the first recorded discovery of gold in the Rocky Mountain region. Unimpressed, his party hurries on to the California goldfields. |

### 1840s

| Year | Date | Event |
| 1849 | August 21 | Proprietor William Bent destroys Bent's Fort. |
| 1849 | March 10 | The Mormon settlers of the Great Salt Lake Valley form the Provisional Government of the State of Deseret. Brigham Young is elected Governor. Deseret encompasses almost all of the present U.S. states of Utah and Nevada, and portions of Oregon, Idaho, Wyoming, Colorado, New Mexico, Arizona, and California, although only the Wasatch Front was occupied. Deseret served as the de facto government of the Wasatch Front until the Provisional State was dissolved on April 4, 1851. |
| 1849 | March 14 | Ute warriors kill mountain man Bill Williams in the San Luis Valley following the Frémont expedition. |
| 1848 | December 22 | Ignoring a warning from guide Bill Williams, John C. Frémont's private expedition for a proposed St. Louis to San Francisco railroad along the 38th parallel north becomes mired in snow of the La Garita Mountains. Ten men and 160 mules will die in the debacle. |
| 1848 | February 2 | The United States and United Mexican States sign the Treaty of Guadalupe Hidalgo to end the Mexican–American War. Mexico relinquishes all of its northern territories. All land in the future State of Colorado becomes unorganized United States territory. |
| 1847 | January 19 | U.S. civilian governor Charles Bent is killed by a band of insurgents at his home in Taos. First Secretary Donaciano Vigil assumes office as the second U.S. civilian governor of New Mexico. |
| 1846 | September 25 | General Stephen Kearny and troops depart for California. Colonel Sterling Price assumes command as the second U.S. military governor of New Mexico. |
| 1846 | September 22 | General Stephen Kearny appoints Charles Bent as the first U.S. civilian governor of New Mexico. |
| 1846 | August 18 | The 1,700 man Army of the West under the command of Brigadier General Stephen Kearny seizes the Nuevo México capital of Santa Fe with little resistance. General Kearny assumes command as the first U.S. military governor of New Mexico. |
| 1846 | July 31 | General Stephen Kearny stages troops of the Army of the West at Bent's Fort for an invasion of Santa Fe de Nuevo México. |
| 1846 | May 13 | U.S. President James K. Polk signs An act providing for the prosecution of the existing war between the United States and the Republic of Mexico. |
| 1846 | April 25 | The Thornton Affair becomes the first skirmish of the Mexican–American War. |
| 1846 | February 14 | The State of Texas cedes the territorial claims of the Republic of Texas to the United States. The boundaries of the State of Texas within that territory remain undefined. The United States now claims the Rio Grande as its border with Mexico. |
| 1845 | December 29 | U.S. President James K. Polk signs the Joint resolution for the admission of the State of Texas into the Union. The Mexican Republic asserts that the annexation is a violation of the Treaty of Limits. This dispute will lead to the Mexican–American War. |
| 1842 | June 10 | U.S. Army Lieutenant John C. Frémont, guide Kit Carson, and cartographer Charles Preuss begin a two-year survey of the High Plains. Maps created by the survey will become guides for the South Platte Trail. |

### 1830s

| Year | Date | Event |
| 1838 | October 6 | The American Fur Company closes Fort Jackson. The fort is destroyed to prevent its use by competitors. |
| 1837 | spring | Frontier trader Ceran de Hault de Lassus de Saint Vrain establishes Fort Saint Vrain at the confluence of the South Platte River with Saint Vrain Creek. |
| 1837 | spring | Frontier traders Peter A. Sarpy and Henry Fraeb establish Fort Jackson on the South Platte River for the American Fur Company. |
| 1837 | March 6 | U.S. Secretary of State John Forsyth accepts the credentials of William H. Wharton as Republic of Texas Minister to the United States of America. Mexico protests the United States recognition of the Republic of Texas as a violation of the Treaty of Limits of 1828. |
| 1836 | May 14 | Texians force captured General Santa Anna to sign the coerced Treaties of Velasco recognizing the independence of the Republic of Texas. Mexico neither acknowledges nor ratifies these treaties. Based upon these treaties, the Republic of Texas claims as its eastern and northern border the Adams–Onís border with the United States and as its western and southern border the Rio Grande to its headwaters, thence north along meridian 107°32′35″ west to the Adams–Onís border with the United States. The disputed region will later become portions of the future U.S. states of Wyoming, Colorado, Kansas, Oklahoma, Texas, and New Mexico. |
| 1836 | March 2 | Texians, Anglo-American immigrants in the Mexican state of Coahuila y Tejas, declare their independence as the Republic of Texas. |
| 1836 | spring | Frontier trader Lancaster Lupton establishes Fort Lancaster on the South Platte River 12 miles (19 km) upstream from Saint Vrain Creek. |
| 1835 | October 2 | The Texian Revolt begins with the Battle of Gonzales. |
| 1835 | spring | Frontier traders Louis Vasquez and Andrew Sublette establish Fort Vasquez on the South Platte River. |
| 1833 | spring | Frontier trader William Bent establishes Bent's Fort on the north bank of the Arkansas River, the United States-Mexico border. The fort serves fur traders and travelers on the Santa Fe Trail. The fort is the first American establishment in the future State of Colorado. |

### 1820s

| Year | Date | Event |
| 1828 | January 12 | The United States and the United Mexican States sign the Treaty of Limits, affirming the border established between the United States and the Spanish Empire by the Adams–Onís Treaty. |
| 1821 | December 26 | Spanish Governor Facundo Melgares receives orders that Santa Fe de Nuevo México is now an intendance of the Mexican Empire. Melgares swears fealty to the empire and becomes the first Mexican Governor of Santa Fe de Nuevo México. |
| 1821 | September 1 | William Becknell and a party of frontier traders leave New Franklin, Missouri bound for Santa Fe by way of the upper Arkansas and Purgatoire rivers. The Becknell route will become the Mountain Branch of the Santa Fe Trail. |
| 1821 | August 24 | The Spanish Empire signs the Treaty of Córdoba recognizing the independence of the Mexican Empire. The Spanish portion of the future state becomes part of the Mexican territory of Santa Fe de Nuevo México, although there is no permanent Mexican presence north of the 37th parallel north. |
| 1821 | August 10 | U.S. President James Monroe certified that the conditions for statehood had been fulfilled and issued Proclamation 28 — Admitting Missouri into the Union. The remaining northwestern portion of the Territory of Missouri becomes unorganized territory. |
| 1821 | March 2 | U.S. President James Monroe signs An Act to authorize the people of the Missouri territory to form a constitution and state government, and for the admission of such state into the Union on an equal footing with the original states, and to prohibit slavery in certain territories. |
| 1821 | February 22 | The Adams–Onís Treaty of 1819 takes effect. The United States relinquishes all land in the future State of Colorado southwest of the Arkansas River or west of the meridian 106°20'35" west. The rest of the future state remains part of the Territory of Missouri. |
| 1820 | July 14 | Edwin James and two other members of a U.S. Army expedition led by Major Stephen Long make the first recorded (White) ascent of Pikes Peak. Major Long names the mountain James Peak. |
| 1820 | March 6 | U.S. President James Monroe signs the Missouri Compromise. The bill allows Missouri to become a slave state, but prohibits slavery in the western territories north of the parallel 36°30′ north. |

### 1810s

| Year | Date | Event |
| 1819 | spring | Spanish Governor Facundo Melgares orders the construction of a military fort near Sangre de Cristo Pass to block a possible invasion of Santa Fe de Nuevo México from the United States. The fort becomes the only Spanish establishment in the future State of Colorado, only to be abandoned in 1821. The U.S. invasion of Nuevo México will not occur until 1846. |
| 1819 | February 22 | The United States and the restored Kingdom of Spain sign the Adams–Onís Treaty The United States relinquishes its claim to land west of the 100th meridian west of Greenwich and south and west of the Arkansas River and south of the 42nd parallel north. Spain relinquishes Florida and all claims to land north of the 42nd parallel in North America. |
| 1812 | June 4 | U.S. President James Madison signs An Act providing for the government of the territory of Missouri. The Territory of Louisiana is renamed the Territory of Missouri. |
| 1810 | August 1 | Mexican priest Miguel Gregorio Antonio Ignacio Hidalgo-Costilla y Gallaga Mandarte Villaseñor (Hidalgo) proclaims the independence of Mexico from the Napoleonic Kingdom of Spain in the village of Dolores. |
| 1810 | | Zebulon Pike publishes The expeditions of Zebulon Montgomery Pike to Headwaters of the Mississippi River, through Louisiana Territory, and in New Spain, during the Years 1805-6-7. His journals will become a popular guide to the Upper Mississippi Basin, the Great Plains, and the Southern Rocky Mountains. |

### 1800s

| Year | Date | Event |
| 1807 | February 26 | Spanish cavalrymen arrest the U.S. Army reconnaissance expedition led by Captain Zebulon Pike in the San Luis Valley. The reconnaissance party will be taken to Santa Fe, then Chihuahua, before being expelled from Nueva España on July 1, 1807. |
| 1806 | November 27 | Zebulon Pike abandons his attempt to climb the summit of the Mexican Mountains (Southern Rocky Mountains) now known as Pikes Peak. Pike will later write that the mountain "may be the highest on Earth". (Twenty-nine peaks are higher in Colorado alone.) |
| 1806 | November 15 | A U.S. Army reconnaissance expedition led by Captain Zebulon Pike first sights the "great summit" of the "Mexican Mountains" that will later bear his name. |
| 1805 | March 3 | U.S. President Thomas Jefferson signs An Act further providing for the government of the district of Louisiana. The District of Louisiana is reorganized as the self-governing Territory of Louisiana. The Territory of Louisiana includes all land in the future State of Colorado in the Mississippi River watershed including the disputed area southwest of the Arkansas River. |
| 1804 | October 1 | The District of Louisiana is reorganized under the jurisdiction of the Territory of Indiana. |
| 1804 | March 26 | U.S. President Thomas Jefferson signs An Act erecting Louisiana into two territories, and providing for the temporary government thereof. The portion of the Louisiana Purchase north of the 33rd parallel north is designated the military District of Louisiana. |
| 1803 | December 20 | French Governor Pierre Clement de Laussat transfers control of La Louisiane to U.S. Governor William Claiborne in a ceremony at La Nouvelle-Orléans (New Orleans) only 20 days after the transfer of Spanish control. The United States and Spain disagree over the western boundary of the territory. The United States maintains that Louisiana includes the Mississippi River and its entire western drainage basin. Spain maintains that its territory includes (1) all land west of the Continental Divide of the Americas including Alta California, and (2) all land south of the Arkansas River and west of the Medina River including Santa Fe de Nuevo México, and (3) all land south of the Red River and west of the Calcasieu River including Tejas. The area in dispute includes land in the future State of Colorado southwest of the Arkansas River but east of both the Continental Divide and the Sangre de Cristo Divide. |
| 1803 | November 30 | Spanish Governor Juan Manuel de Salcedo transfers control of La Luisiana to French Governor Pierre Clement de Laussat in a ceremony at Nueva Orleans (New Orleans). This formal transfer of power was made solely to accommodate the Louisiana Purchase. |
| 1803 | April 30 | The United States and the French Republic sign the Louisiana Purchase Treaty. Wishing to guarantee American navigation rights on the Mississippi River, U.S. President Thomas Jefferson had offered to purchase the Mississippi River port of New Orleans from the French Republic. Concerned with the potential cost of future campaigns, French First Consul Napoléon Bonaparte countered with an offer to sell the entire territory of La Louisiane to the United States for 80 million French francs or $15 million U.S. dollars. |
| 1801 | March 21 | The French Republic and the Spanish Empire sign the Treaty of Aranjuez setting the terms for the "restoration of La Louisiane to France." |
| 1800 | October 1 | Seeking to restore French presence in the Americas, French First Consul Napoléon Bonaparte pressures King Carlos IV of Spain to agree to the secret Third Treaty of San Ildefonso to transfer La Luisiana to the French Republic in exchange for French claims in Tuscany. |

### 1790s

| Year | Date | Event |
| 1792 | October 3 | French frontiersman Pierre "Pedro" Vial arrives in Saint-Louis from the Spanish settlement of Santa Fe. The route he followed will become the Cimarron Branch of the Santa Fe Trail. |

### 1780s

| Year | Date | Event |
| 1789 | March 4 | The new Constitution of the United States takes effect as the 1st United States Congress convenes. |
| 1783 | September 3 | The Treaty of Paris is signed in Paris by representatives of King George III of Great Britain and representatives of the United States of America. The treaty affirms the independence of the United States and sets the Mississippi River as its western boundary. |

### 1770s

| Year | Date | Event |
| 1778 | | Bernardo de Miera y Pacheco, cartographer for the Dominguez–Escalante Expedition, publishes his map of the expedition across the Colorado Plateau. His map becomes the foundation of a future trade route later known as the Old Spanish Trail. |
| 1776 | July 29 | A Spanish-Franciscan expedition led by Franciscan priests Francisco Atanasio Domínguez and Silvestre Vélez de Escalante sets out from La Villa Real de la Santa Fé de San Francisco de Asís (Santa Fe) in search of an overland route to the Presidio Reál de San Carlos de Monterey (Monterey). The expedition follows the 1765 route of Juan Rivera northwest across the Colorado Plateau. The expedition fails to reach Las Californias, but reaches the lower Paria River in the future State of Arizona before returning to Santa Fe. |
| 1776 | July 4 | Representatives of the thirteen United States of America sign the Declaration of Independence from the Kingdom of Great Britain. |

### 1760s

| Year | Date | Event |
| 1765 | July | Governor Tomás Vélez Cachupin of Santa Fe de Nuevo México dispatches an expedition led by Juan Maria Antonio Rivera to explore the San Juan Mountains and the Colorado Plateau. |
| 1764 | September 30 | The secret Treaty of Fontainebleau is proclaimed. This ends the competition between France and Spain on the Great Plains. |
| 1763 | September 30 | The Treaty of Paris is signed ending the Seven Years' War and the French and Indian War. The Kingdom of Great Britain acquires the land east of the Mississippi River. |
| 1762 | November 23 | Fearing the loss of all his North American territories as a result of the Seven Years' War (the French and Indian War in North America), King Louis XV of France makes the secret Treaty of Fontainebleau transferring La Louisiane to his cousin King Carlos III of Spain. |

### 1730s

| Year | Date | Event |
| 1739 | July 5 | On a voyage up the Arkansas River to the confluence of the Purgatoire River (in the future State of Colorado), Pierre Antoine and Paul Mallet encounter an Arikara man who agrees to guide them to Santa Fe. This is the first contact between France and Spain in the Rocky Mountain region. |

### 1720s

| Year | Date | Event |
| 1720 | August 6 | A Spanish expedition led by Don Pedro de Villasur seeking information about the French in the area reaches the South Platte River, called by the Spanish the Río Jesús María. They continued northeast into Nebraska where the expedition was largely destroyed in an attack by a group of Pawnee people on 14 August. |

### 1700s

| Year | Date | Event |
| 1707 | May 1 | The Treaty of Union takes effect uniting the Kingdom of England and the Kingdom of Scotland as the Kingdom of Great Britain. |

### 1690s

| Year | Date | Event |
| 1692 | September 14 | Diego de Vargas Zapata y Luján Ponce de León y Contreras completes the reconquest of the Spanish colony of Santa Fe de Nuevo Méjico to end the Pueblo Revolt. |

### 1680s

| Year | Date | Event |
| 1682 | April 9 | René-Robert Cavelier, Sieur de La Salle, claims the Mississippi River and its watershed for the Kingdom of France and names the region La Louisiane in honor of King Louis XIV. The Mississippi Basin is later determined to be the fourth most extensive on Earth and includes lands inhabited by hundreds of thousands of native peoples and lands previously claimed by Spain, France, and England. The Louisiane claim includes all land in the future State of Colorado east of the Continental Divide of the Americas and the Sangre de Cristo Mountains. This will set up a rivalry among native peoples, France, Spain, and eventually the United States in the area. |
| 1680 | August 13 | Tewa shaman Popé of Ohkay Owingeh leads the Pueblo Revolt against the Spanish rulers of Santa Fe de Nuevo Méjico. The Spanish settlers flee down the Rio Grande to El Paso del Norte. |

### 1590s

| Year | Date | Event |
| 1598 | July 12 | Don Juan de Oñate Salazar establishes the New Spain (Nueva España) colony of Santa Fe de Nuevo Méjico at the village of San Juan de los Caballeros adjacent to the Ohkay Owingeh Pueblo at the confluence of the Rio Grande (río Bravo) and the río Chama. At its greatest extent, the colony encompassed all of the present U.S. state of New Mexico and portions of Arizona, Utah, Colorado, Wyoming, Nebraska, Kansas, Oklahoma, Texas, and the Mexican state of Chihuahua. |

### 1540s

| Year | Date | Event |
| 1541 | June 28 | A Spanish military expedition led by Hernando de Soto, Governor of Cuba, become the first Europeans to cross the Mississippi River. |
| 1541 | spring | The Spanish military expedition led by Francisco Vásquez de Coronado leaves the Tiwa pueblos and searches the Great Plains for Quivira. The expedition may, or may not, have crossed the southeast corner of the present U.S. State of Colorado. |
| 1541 | winter | The Tiwa resist the occupation by the Coronado expedition, but hundreds are killed in the Tiguex War. |
| 1540 | autumn | The military expedition led by Francisco Vásquez de Coronado, reaches the Tiwa pueblos along the Río Bravo (Rio Grande). The expedition occupies several of the pueblos. |
| 1540 | July 7 | The military expedition led by Francisco Vásquez de Coronado, reaches the Zuni pueblo of Hawikuh. The Zuni resist but are driven off by the Spanish soldiers. |
| 1540 | February 23 | Francisco Vásquez de Coronado, Governor of Nueva Galicia, departs Compostela, México commanding a Spanish military expedition of 400 soldiers and 1,300 to 2,000 Mexican Indian allies in search of the Seven Cities of Cibola. |

### 1520s

| Year | Date | Event |
| 1520 | August 13 | Spanish conquistador Hernán Cortés defeats Aztec Emperor Cuauhtémoc, seizes Tenochtitlán, and proclaims the establishment of Nueva España (New Spain). |

### 1510s

| Year | Date | Event |
| 1519 | autumn | A Spanish naval expedition along the northeastern coast of Mexico charts the mouths of several rivers including the Río de Nuestra Señora (Rio Grande). |
| 1513 | September 29 | Spanish conquistador Vasco Núñez de Balboa crosses the Isthmus of Panama and arrives on the shore of a sea that he names Mar del Sur (the South Sea, later named the Pacific Ocean). He claims the sea and all adjacent lands for the Queen of Castile. This includes the portion of the future State of Colorado west of the Continental Divide of the Americas. |

### 1490s

| Year | Date | Event |
| 1493 | May 4 | After receiving accounts of the voyage of Columbus, Pope Alexander VI (born Roderic de Borja in Valencia) issues the papal bull Inter Caetera that splits the non-Christian world into two halves for Christian exploration, conquest, conversion, and exploitation. The eastern half goes to the King of Portugal and the western half (including almost all of the Americas) goes to the Queen of Castile and the King of Aragon. The indigenous peoples of the Americas have no idea that any of these people exist. |
| 1492 | October 12 | Genoese seaman Christopher Columbus (Cristòffa Cómbo) lands on the Taíno island of Guanahani in the Bahamas which he renames San Salvador and claims for Queen Isabel I of Castile and the King Fernando II of Aragon. This begins the Spanish conquest of the Americas. |

### Before 1492

| Era | Event |
| 1300–1525 CE | Jicarilla Apache migrate to the southern extent of the Rocky Mountains from Alaska and Northwestern Canada. |
| 1275–1300 CE | A prolonged drought on the Colorado Plateau forces many Ancestral Puebloans to migrate southeast into the Rio Grande Valley. |
| c. 1150 CE | The Slumgullion Earthflow dams the Lake Fork to form Lake San Cristobal, presently the second largest natural lake in Colorado. |
| c. 1100 CE | Ancestral Puebloans begin construction of cliff houses on Mesa Verde. |
| c. 550 CE | Ancestral Puebloans move onto Mesa Verde. |
| c. 2140 BCE | The Dotsero Volcano erupts, the most recent volcanic eruption in the future State of Colorado. |
| c. 4900 BCE | Paleoamericans camp at the Magic Mountain site near Golden. |
| c. 8670 BCE | Paleoamericans of the Folsom culture camp at the Lindenmeier site in present-day Larimer County. |
| c. 11,500 BCE | During the Allerød oscillation, Paleoamericans from Beringia begin using the ice-free corridor east of the Rocky Mountains to migrate throughout North America. New research indicates the Colorado region may have been visited much earlier via the Pacific Ocean. |