About 2.5 minutes into the movie, the lover changes from street shoes to boots, attempting to plant a false trail. He first changes his right shoe and then hands a second right shoe to the wife.
The missing persons report misspells "ninety" as "ninty."
Right after Carson first sees Duncan's car drive by (after Duncan has spotted him in the plane), there are two cars on the side of the dirt road in the background. Since Carson is supposed to be in the middle of the deserted desert, and would presumably ask the people in the cars for help or wait until they got back, it's safe to assume that these are crew vehicles.
When Robert Ryan is first seen, alone and injured in the desert, he expects his wife and her lover to return for him. The second time he is shown, he is certain that they have abandoned him and has clearly felt so for some time. There is no transition between the two feelings, no moment shown when he realizes the truth, though that would have provided a very dramatic moment.
Early in the movie, after Robert Ryan has put a splint on his broken leg (which continues to cause him a lot of pain), he takes a small branch and breaks it over the injured leg, seemingly without feeling any pain.