Here are a couple of photos from my cyclocross race at the Boulder Reservoir. A 45-minute race at top speed - or as fast as you can navigate the course (sand, mud, gravel, grass, pavement) and get through the obstacles (barriers, logs, more sand):


If you are not familiar with the sport of cyclocross you can find out more here:
http://en.wikipedia.org/wiki/Cyclo-crossYou can also watch the following video that I put together from last years pro men's race: