The unique endurance sport of pack burro racing, which is a unique blend of trail running and pack burro trekking, has been happening in Colorado since 1949. In 2012, it was designated as Colorado’s official summer heritage sport. The season gets into full swing with four races from July 20 to Aug. 10. A burro race involves a human runner racing alongside a burro for anywhere from about 4 to 29 miles. The adventure lies in how those teams of two get from the starting line to the finish line. Click through the photos below to get a glimpse at this crazy sport.