When the Guide gets bitten by rattlesnakes and the 'mules' are scared, it shows horses running (and naying) away. When he finds a 'mule' it is back to being a mule.
The 'boulder' Lori tries to wedge from from Nick's leg using a dried tree branch is a huge chunk of rock, not a boulder. In between takes it is larger then smaller. Also, this massive rock was not seen falling when they fell from the rock face.
The rescue helicopter has no ID number on the tail or the body, contrary to FAA regulations.
The Vulture shown eating at Henry's body is likely a Griffin Vulture which is only found in the old world. In any event, it is not one of the two vultures that one would likely find in the Grand Canyon (Turkey or Black). Nor is it a Condor.