Part of site selection is researching the nearest hospital or critical care facility. You should also take note of nearby trails, fire roads, etc. that could be used for an evacuation should that be necessary. As rescuers, we always ask ourselves the question - what if? Suppose someone with a preexisting back problem slips, falls, and wrenches their back. Let's face it, we are not properly equipped to transport someone with a C-Spine injury any significant distance. This is especially the case in more wilderness settings like canyons or riversides with thick underbrush. This is why we should pack a cell phone in a waterproof container - to call for help should that be necessary. I also like to pack two copies of a patient assessment form with a pencil in my first aid kit - one stays onsite and the other goes with the runners.
Another major challenge is getting the help and equipment you need (like a backboard and trained personnel). This is where the SOAP form and practice play a vital role. Practice your pitch before running for help. You need to convince that 911 operator you know what you are talking about, else they will need to send an inexperienced scout with a radio.
We boat in some pretty remote areas. Although it is easy for us to head downstream with our boats, picture how difficult it can be traversing up a stream bank with heavy equipment. Helicopter landing sites are not typically close by either. Let's face it, getting the professionals to your accident site can be quite challenging and time consuming. You will also need to provide some sort of weather protection in the meantime to prevent hypothermia.