Yes, one of the hazards of riding out here is open mine shafts. They are often unmarked and occasionally just off the trail. Just off the trail means maybe a foot or so. If you are very unfortunate and going too fast and overshoot a corner..................well you just may end up at the bottome of a 30 ft drop with a bike on top of you. Yes, it happens out here, thankfully not often, but the result is often death.