I applied online. The process took 3 weeks. I interviewed at Canyon Ranch (Tucson, AZ) in Jan 2014
Interview
Phone interview, in person interview, interview hike (basically to see if you can hang on a hike - don't be at the back of the pack), background check, driving records check, physical exam, drug test. You'll be taking everyone from average people to celebrities on back-country hikes so a sense of confidentiality and professionalism is a must.