This is a simple exploit to gank players in AB without having them reach you. I actually do this with my rogue while a friend heals me up the hill. See in the next picture.
This is what you should see. It is in LM area :ImageShack - Hosting :: wowscrnshot090208194317ka5.jpg
Mount up and get on the very left tree on the picture and when you are the end of the branches just jump on the hill in front of you.
Now you can heal or range-dps from a safe place.