Baxter It is a race thru whatever terrain that is available. Usually there will be; hill climbs, mudholes, tight woods, off camber, openfields, a motocross section, creek crossings, and anything else they can find to run you thru that will wear you down.
usually two hours plus one lap in length, but different series do it differently.
Here on the east coast the biggest series is the GNCC. It is common to have 30 to 50 quads per class and last I checked they ran about 12 or so classes. laps will usually be between 3 and 15 miles per lap.