About.com: Wheelchair Mountain Biking
   Directory of resources for mobility-impaired riders to travel mountain bike trails.
   http://mountainbike.about.com/cs/wheelchair/

Grove Innovations
   Builder of mono-skis and off-road mountain wheelchair.
   http://www.sitski.com/grove.html

Popular Mechanics
   Detailing the design of downhill mountain wheelchairs.
   http://popularmechanics.com/popmech/out/9705BOODBM.html