The Four Pass Loop has a strong argument for being one of the most stunning loops in North America. Located outside of Aspen, Colorado, the loop hits four high passes -- Buckskin (12,462'), Trail Rider (12,415'), Frigid Air (12,500'), and West Maroon (12,490'). Most people choose to backpack it in 2-4 days, but it's also a popular 1-day run for many trail runners.
