C.R.S. § 42-4-711

(1) The driver of a motor vehicle traveling through defiles or canyons or on mountain highways shall hold such motor vehicle under control and as near to the right-hand edge of the highway as reasonably possible and, except when driving entirely to the right of the center of the roadway, shall give audible warning with the horn of such motor vehicle upon approaching any curve where the view is obstructed within a distance of two hundred feet along the highway. (2) On narrow mountain highways with turnouts having a grade of six percent or more, ascending vehicles shall have the right-of-way over descending vehicles, except where it is more practicable for the ascending vehicle to return to a turnout. (3) Any person who violates any provision of this section commits a class A traffic infraction.