Predicament: You're scrambling up a talus field when the unexpected happens: A boulder shifts, then slams down on your hand or foot, pinning you in place.
Lifeline: Stay calm. Try to roll the boulder off. Too heavy? Call in a rescue. No phone service? Send a partner for help–but only after he has set you up with shelter, stove, and extra food. (Always assume that a rescue won't happen for at least a day.) While you wait, slowly sip water and take painkillers; after the initial numbness passes, you'll start to hurt. If someone frees you before help arrives, and severe bleeding begins, apply a tourniquet to the affected limb.
If you've been trapped for more than 6 hours, be aware of the possibility of crush syndrome–renal failure and shock caused by the release of toxins built up in the area deprived of blood. Crush syndrome can set in quickly or hours later. Whether it happens or not, your objective is the same: to get medical attention fast. Your evacuation plan will depend on your ability to walk and your distance from the trailhead.