In preparation for the alien role,
Jeff Bridges studied birds, borrowing their sudden jerky head movements among other subtle nuances to add to his character. This of course translated well, since this alien would not have natural human mannerisms, being "encased" in a human's body for the first time.
The "rendez-vous" point Jeff Bridges and Karen Allen climed down into, to meet up with his ship, is a crater located outside Flagstaff, Arizona and is about 49,000 years old, 570 feet deep, and a mile wide. The equivelant force of 20 to 40 million tons of TNT from a 100-165 foot diameter asteriod resulting in the force of an atomic bomb. (Information from National Geographic)