North Boulder Creek forms in a valley between Navajo Peak and Arikaree Peak on the Continental Divide, in the Green Lakes chain of lakes.

On the east edge of the city, the creek receives South Boulder Creek, which rises at Rogers Pass on the Continental Divide, just south of the Moffat Tunnel.

[2] After leaving the city, Boulder Creek flows northeast into Weld County, where it joins St. Vrain Creek, and on to a confluence with the South Platte River.

Boulder Creek is a summer recreational spot for outdoor activities including tubing, fly fishing, and wading.

The annual Boulder Creek Festival, held along the creekside civic area between the library and Central Park, opens the summer season on Memorial Day weekend.