After riding 520 miles of the 534-mile event (known as the "Longest Off-Road Race in the United States"), Longson crashed his Yamaha after hitting what appears to be loose gravel over the trail. The incident occurs at the 4:30 mark of the video, at which point Longson flies back-first into the rock-strewn terrain.
Being in such a remote location meant Longson was far from help, so he hopped back on his bike, took a quick breather and headed for the finish line. Through the rest of the video, you hear him groaning in pain as he rides over the rough terrain. Despite all that, he finished the race in 38th place overall and third in his class.
The ordeal, recorded on Longson's helmet camera, is posted below. Note that the audio contains some explicit language, particularly (and understandably) in the portion following the crash.