The steepest mile of the top cycling climbs in Colorado. From this page you may navigate to the top 10 steepest bicycling climbs in CO. Colorado's steepest bike climbs we have documented are featured in the slideshow below. Scroll down to access Colorado's steepest mile Top 10 Bicycle Climbs "Table". The cycling climbs covering the steepest mile gradients in CO, and some of Colorado's hardest and most scenic cycling climbs are, in order of steepness, 1. East Portal, 2. Flagstaff Rd, 3. Magnolia Road, 4. Super Flag, 5. Rist Canyon West, 6. Sugarloaf Rd , 7. Linden Avenue, 8. Left Hand Canyon - Jamestown - Brainard, 9. Pikes Peak, and 10. Lee Hill - Deer Trail.