Mountain unicycles can be ridden on the same terrain as a mountain bike. Mountain unicycling is a slower-paced sport than mountain bicycling, since unicycles are more difficult to ride than bicycles, and cannot coast.
Events
Each year, many unicyclists gather for the California Mountain Unicycle Weekend.
History of Mountain-unicycling
Mountain unicycling has been around for a while; a more detailed history should go here.
External links: http://www.extremeunicycling-bcmat.cityslide.com/