It wasn't long before tents, tepees, wagons, lean-tos, and crudely constructed log cabins lined the banks of the South Platte River as prospectors and fortune-seekers poured into the area. They came from all over the country, traveling on foot, in covered wagons, by horseback, and even pushing their belongings in wheelbarrows. Pikes Peak, a 14,000-foot mountain to the south of the mining camp served as both a landmark and a rallying cry for weary travelers. The "Pikes Peak or Bust!" gold rush was in full force.
However, gold wasn't the only way to strike it rich in the boomtown that was springing up on the banks of the South Platte. Those who arrived early enough could simply stake out a claim of land, lay out city streets, and then sell the lots to those arriving after them. General William H. Larimer didn't arrive early but followed the plan perfectly. He claim-jumped the land on the eastern side of Cherry Creek, laid out a city and, in hopes of gaining political favor, named the city after Kansas Territorial governor James Denver. What he didn't know was that Denver had already resigned.
A great fire burned much of Denver's business district to the ground in 1863. The following year, a flash flood swept down Cherry Creek, killing 20 people and causing a million dollars in damage. And shortly after that, an Indian war broke out, cutting stage stations and supply lines and leaving Denver with just six weeks of food.
The early hardships only solidified the resolve of Denver's citizens and made them more determined to not just survive but to thrive. When the Union Pacific Railroad bypassed Colorado on its transcontinental route, Denverites raised $300,000 and built their own railroad to meet the Union Pacific in Cheyenne, Wyoming. Soon after, the Kansas Pacific Railroad crossed the plains to Denver and, when a major silver strike was hit in Leadville, Denver was a boomtown once again.
Pike's Peak Gold Rush
In the summer of 1858, during the Pike's Peak Gold Rush, a group of gold prospectors from Lawrence, Kansas established Montana City as a mining town on the banks of the South Platte River in what was then western Kansas Territory. This was the first historical settlement in what was later to become the city of Denver.
Arapahoe County was formed on November 1, 1861, and Denver City was incorporated on November 7, 1861.
Read more here https://en.wikipedia.org/wiki/Pike%27s_Peak_Gold_Rush
Colorado during the Civil War
The Colorado Territory was formally created in 1861 shortly before the bombardment of Fort Sumter sparked the American Civil War. Although sentiments were somewhat divided in the early days of the war, Colorado was only marginally a pro-Union territory (four statehood attempts were thwarted, largely by Confederate sympathizers in July 1862, February 1863, February 1864, and January 1866).
Colorado was strategically important to both the Union and Confederacy because of the gold and silver mines there as both sides wanted to use the mineral wealth to help finance the war. The New Mexico Campaign (February to April 1862) was a military operation conducted by Confederate Brigadier General Henry Sibley to gain control of the Southwest, including the gold fields of Colorado, the mineral-rich territory of Nevada and the ports of California. The campaign was intended as a prelude to an invasion of the Colorado Territory and an attempt to cut the supply lines between California and the rest of the Union. However, the Confederates were defeated at the Battle of Glorieta Pass in New Mexico and were forced to retreat back to Texas, effectively ending the New Mexico Campaign.
During the late 1850s, many Southerners migrated to the Colorado Territory in search of new opportunities, including working in the newly discovered gold fields. When the War broke out, many returned to the South to defend their homes. However, some remained and formed militia groups in Fairplay, Leadville, Denver and Mace's Hole (present day Beulah). These Confederate Partisan Ranger units operated in the Colorado Territory from 1861 to 1865, raiding supply wagon trains, disrupting communications lines, recruiting volunteers, and skirmishing with Union troops.
When President Abraham Lincoln called for volunteer soldiers to supplement the Regular Army, Colorado residents responded, with nearly 4,000 men eventually enlisting in the volunteer Union forces authorized by the United States War Department. Hundreds more served in militia companies, authorized by the territorial governor, most of which were formed to fight Indians rather than Confederates. Three regiments of infantry were organized, which were reorganized as two regiments of cavalry, while a third regiment of cavalry was raised in 1864. Other residents enlisted in New Mexico units.
Territory of Colorado
The Territory of Colorado's boundaries were identical to the current State of Colorado. The territory ceased to exist when Colorado was admitted to the Union as a state on August 1, 1876. The territory was organized in the wake of the 1859 Pike's Peak Gold Rush, which had brought the first large concentration of white settlement to the region. The organic act creating the territory was passed by Congress and signed by President James Buchanan on February 28, 1861, during the secessions by Southern states that precipitated the American Civil War. The organization of the territory helped solidify Union control over a mineral rich area of the Rocky Mountains.
East of the divide, the new territory included the western portion of the Kansas Territory, as well as some of the southwestern Nebraska Territory, and a small parcel of the northeastern New Mexico Territory. On the western side of the divide, the territory included much of the eastern Utah Territory, all of which was strongly controlled by the Ute and Shoshoni. The Eastern Plains were held much more loosely by the intermixed Cheyenne and Arapaho, as well as by the Pawnee, Comanche and Kiowa. In 1861, ten days before the establishment of the territory, the Arapaho and Cheyenne agreed with the U.S. to give up most their areas of the plains to white settlement but were allowed to live in their larger traditional areas, so long as they could tolerate homesteaders near their camps. By the end of the American Civil War in 1865, the Native American presence had been largely eliminated from the High Plains.
Statehood was regarded as fairly imminent, as during the run-up to the 1864 presidential election the Republican–controlled Congress was actually eager to get two more Republican senators and three more electoral votes for President Lincoln's re-election bid. Territorial Governor John Evans persuaded Congress to adopt an enabling act, but a majority of the 6,192 Coloradoans who voted, in a population of around 35,000, turned down the first attempt at a state constitution and the second attempt at statehood. Later, at the end of 1865, territorial ambitions for statehood were thwarted again, this time by a veto by President Andrew Johnson. Statehood for the territory was a recurring issue during the Ulysses Grant administration, with Grant advocating statehood against a less willing Congress during Reconstruction.
Read more here https://en.wikipedia.org/wiki/Colorado_Territory
The Colorado War (1863–1865) was an armed conflict between the United States and a loose alliance among the Kiowa, Comanche, Arapaho, and Cheyenne nations of Native Americans (the last two were particularly closely allied). The war was centered on the Eastern Plains of the Colorado Territory and resulted in the removal of these four Native American peoples from present-day Colorado to present-day Oklahoma. The war included a particularly notorious episode in November 1864 known as the Sand Creek Massacre. The battle, initially hailed by the U.S. press as a great victory, was later learned to be one of genocidal brutality. The resulting hearings in the United States Congress regarding the malfeasance of the U.S. Army commander, John Chivington, were a watershed in the white views of the Indian Wars at the close of the American Civil War. In 1868 the U.S. Army, led by George Armstrong Custer, renewed the conflict against the Arapaho and Cheyenne at the Battle of Washita River.
Read more here https://en.wikipedia.org/wiki/Colorado_War
Denver Pacific Railway
The first train from Cheyenne arrived in Denver on June 24, 1870. Two months later, in August 1870, the Kansas Pacific completed its line to Denver and the first train arrived from Kansas. The Denver Pacific line intersected the Kansas Pacific at "Jersey Junction", three miles north of downtown Denver. With the completion of the Kansas Pacific line to Denver (completed at Strasburg on the Colorado Eastern Plains), the Denver Pacific became integral to the first transcontinental rail link between the east and west coasts of America. While the Union Pacific line had been declared finished in 1869 with the Golden spike event in Utah, linking it with the Central Pacific Railroad, passengers were required to disembark the train and cross the Missouri River at Omaha by boat. With the completion, it was finally possible to embark a train on the east coast and disembark on the west coast.
Finally linked to the rest of the nation by rail, Denver prospered as a service and supply center. The young city grew during these years, attracting millionaires with their mansions, as well as a mixture of crime and poverty of a rapidly growing city.