The Flatirons are rock formations in the western United States, near Boulder, Colorado, consisting of flatirons. There are five large, numbered Flatirons ranging from north to south along the east slope of Green Mountain, and the term "The Flatirons" sometimes refers to these five alone. Numerous additional named Flatirons are on the southern part of Green Mountain, Bear Peak, and among the surrounding foothills.

Boulder is a home rule city and the county seat of Boulder County, Colorado, United States. It is the largest city in Boulder County, with a population of 108,250 at the 2020 United States census, making it the 12th-most populous city in Colorado. Boulder is the principal city of the Boulder, CO Metropolitan Statistical Area and part of the Front Range Urban Corridor.