More than 3,600 runners took to the streets for the half marathon alone in this suburb of the Denver metropolitan area at the spring 2010 running of Denver's Colorado Colfax Marathon & Half Marathon, whose 13.1-mile race features a long, straight out-and-back course that starts and finishes at Denver's City Park and takes runners along two long parallel straightaway runs from the park to the turnaround and back, including some gradual elevation climbs.