More than 150 years ago, the Barr Lake area was a bison wallow where bison, wolves and elk gathered, taking advantage of available water. Nearby, pronghorn antelope roamed the fertile mixed-grass prairie. All this wildlife brought Native American tribes like the Arapaho, Cheyenne and Ute to the area. They would come here at different times of the year to hunt and find food.

• 1860s: Cowboys and Spanish steers move to the Barr Lake area. The wallow is an important rest stop on the way from Texas to Wyoming on the Goodnight-Loving Trail.
• 1883: The Chicago, Burlington and Quincy railroads complete a link between Denver and Chicago that passes right by the Barr Lake area. Suddenly, this prairie oasis is ripe for settlement — if only there were a reliable source of water. 
• 1886: Construction begins on the Burlington Canal, a reliable water source for settlers. The canal diverts water from the South Platte River into the wallow to create Oasis Reservoir. The grassy landscape next to the reservoir becomes a cottonwood forest, creating an important refuge for wildlife. 
• 1908: The Farmers Reservoir and Irrigation Company increases the size of Oasis Dam. The new dam combines Oasis Reservoir and the smaller Burlington Reservoir to create what is now known as Barr Lake. With a reliable water source, local sugar-beet farmers are soon producing "more gold than all the miners in the mountains."
• 1964–1965: Clean water legislation and the flood of ’65 flushes Barr Lake clean after over 70 years of pollution from Denver’s untreated wastewater.
• 1975: Colorado Parks and Wildlife receives a recreational lease for Barr Lake State Park.
• 1977: Barr Lake State Park opens to the public.