A Klondike derby is an annual event held by some Boy Scouts of America councils during the winter months, usually January.
Each troop within the council brings a dog sled (sans sled dogs), usually one constructed as a troop project. The troop pulls their sled around the hosting campground or Scout reservation, visiting stations that are typically named after Alaskan towns. At each station, skills and knowledge are demonstrated to the station-masters (or 'mayors') on such topics as American history, ropework and knot-tying, proper use of tools, first-aid, map-reading, and fire-building. Points are awarded based on performance. At the end of the event, the troops with the highest point totals are recognized in an awards ceremony.
To get a good idea of what a Klondike derby is like for an average scout, imagine lugging a 150 pound sled around for 8 hours, completing mundane tasks while racing around as fast as you can, then after doing all that construct a shelter you can live in (usally in below-freezing temperatures), without any food or water except for the twenty minutes you have to prepare a meal from scratch in the middle of the snow.
Sleds in the Klondike derby can be made of anything from wood to plastic piping. They may run on small detachable wheels in the event of a snow-free Derby.