Your Own Personal Time Trial
With “regular” cross, at least in my limited experience (two races), you are absolutely red-lined from the start. Typically my race would begin with royally screwing up clipping into the pedals, causing a blockade to those riders behind me, while the lead racers are already 30 meters up the course. “Hole shotting” aka getting a great start, is a pretty big deal in “regular” cyclocross.
Unlike “regular” cyclocross racing, where competitors hammer themselves around a short course for multiple laps, for an hour at worse, Ultra CX goes beyond that. Ultra CX competitors typically face an open road type course, featuring paved roads, gravel roads, sludge pits and hike-a-bike sections. The shortest race is usually around three and a half hours in length, with some events such as the Dirty Kanza, stretching to over 12 hours for most competitors, with 200 miles of terrain to traverse.