In 2005, the city began experimenting with using goats for weed control in environmentally sensitive areas. Goats naturally consume diffuse knapweed and Canada thistle, and although the program was not as effective as it was hoped, goats were used again in 2010 to keep weeds under control at the Boulder Reservoir and will be considered in the future for weed control projects.

Boulder Creek is the primary flow of water through Boulder. A tributary of the South Platte River, the creek was named for all of the large granite boulders that have cascaded into the creek over the years. It is from Boulder Creek that Boulder city is believed to have taken its name.

Boulder lies in a wide basin beneath Flagstaff Mountain just a few miles east of the continental divide and about 25 miles (40 km) northwest of Denver. The peak, which is located in Boulder Mountain Park, includes hiking and bike trails, picnic areas, the Summit Nature Center, and an outdoor amphitheater.

Clela Rorex had only held the position of county clerk for 3 months when two men, Dave McCord and Dave Zamora, came to the clerk's office to apply for a marriage license. They had originally applied in Colorado Springs, where there were told to go to Boulder because El Paso County didn't do "that type of thing." After consulting with District Attorney Alex Hunter, Rorex was told it was within her legal right to decide if she wanted to issue the license or not. Rorex issued the license on March 26, 1975. She went on to issue five more same-sex marriage licenses in Boulder before the Colorado Attorney General forced her to stop.

Boulder has hosted a 10 km road run known as the Bolder Boulder on Memorial Day every year since 1979. The race involves over 50,000 runners, joggers, walkers, and wheelchair racers, making it one of the largest road races in the world. It culminates at Folsom Field with a Memorial Day Tribute and has the largest non-marathon prize purse in road racing.