It is vital when running trails and you get injured and especially if sweeping at a trail race, that you accurately communicate your location when requesting a Search and Rescue response for a down runner. Trail name, estimated distance and direction from a land mark like a trail junction sign or other land mark are good but could be miss-interpretated or unknown. Latitude and Longitude is more accurate and universal, especially for pilots in a rescue helicopter.

Take your cell phone with you even though there may be no cell service in the mountains and make sure the Location services are turned on (system) which activates the GPS. Turn the cell phone horizontal (landscape mode). Select the Google Maps app and tap the target button to center up your GPS location on the map.

Hold your finger directly on the center button to drop a location pin which will pop up its latitude and longitude in the Search bar or Info panel - you may have to scroll down past any address or other info that pops up. Dont drop the pin on a labeled location. Spreading out the screen can make the pin location a little more accurate and avoid business pop ups.

Sending your latitude and longitude up to 4 decimal places will get responders within shouting distance to your location (34.1775,-118.0457 is within 100 ft on Mt. Wilson Trail at the Charlies New Trail junction right where I was). Make sure your phone is held horizontal and you find the decimal value and not the degree/minutes/seconds readout on the display. The decimal value can be entered directly into the Search Google Maps box in the upper left corner of a computer without spaces (dont forget the minus sign before the longitude or you might show up as being in China.

Those with iPhones, you can use Apple Maps and get it quickly in a similar fashion - video

It is a good idea to do a screen grab of the lat/lon map for future reference or sending the image via text or email when able. Screen grab on Android phones is typically holding the power and volume buttons down at the same time, or holding down the power button for a few seconds and then tapping Screenshot. For iPhones see the video.