Call 911. The dispatcher will be able to determine the nature of the emergency and send the appropriate response.
Stay put. It's much easier to find and rescue someone who is stationary and not moving around.
Before heading into the backcountry, make sure that you have the Ten Essentials:
Navigation - Map, compass, and GPS system
Sun protection - Sunglasses, sunscreen, and hat
Insulation - Jacket, hat, gloves, rain shell, and thermal underwear
Headlamp - Plus extra batteries
First-aid supplies - First aid kit and personal medications
Fire - matches, lighter, and fire starters. Emergency use only!
Knife - plus repair kit
Extra food - beyond minimum expectation
Extra water - beyond minimum expectation, or the means to purify
Emergency shelter - Tent or bivy
Reminder: campfires are not allowed at any time in the San Bernardino National Forest!
San Bernardino National Forest - Check for forest closures and general access information
SoCal Snow - Avalanche & backcountry snow information site
Ben's Weather - Local forecast