From the Bureau of Land Management website http://www.blm.gov/ca/news/newsbytes/xt ... safety.htm
"Stay on Designated Routes"
News.bytes Extra, 3/14/06
Staying on designated routes in remote public land areas of the California Desert became an important lesson for an OHV recreationist and his passenger who fell down a vertical mineshaft last weekend in eastern Imperial County (luckily, a broken arm was the only injury). Traveling off-road in a designated "limited use" area (where travel is restricted to identified safe routes), the two men spent Sunday afternoon and night -- 20 hours total -- down the abandoned mineshaft before being rescued.
BLM arranged to have the vehicle extracted. An investigation is underway.