In spite of all of the training I have had, experience tells me that I always need to plan for communications and trying to get help with evacuating the casualty. First aid, especially in trauma cases, is only to keep them alive until more help arrives or you can get them out. Deep in a canyon with no roads in the Summer, even a sprained ankle can be catastrophic in certain circumstances.
Amen to that.
With anything reasonably serious (the victim is not ambulatory) you need either a helicopter or a crew of eight to sixteen, plus specialized gear (typically something like a wheeled litter) plus time to get to definitive care.
My experience was before cell phones were common, but typically ambulatory victims ambled out, and SAR was notified for those who were immobilized. Thank heaven for helicopters! They save time, effort, and lives.
Today cell phones or something more sophisticated make response both quicker and more efficient. The SAR team goes in with a much better understanding of the situation.