On the night of July 30, 1971 during the Apollo 15 moon landing the moon is depicted as full. On this date the moon was in its first quarter.
Early on, Bernadette Manuelito receives a letter addressed from the "U.S. Customs and Border Protection." The agency wasn't known as this until 2003. At the time period the filming says (1971), the agency was simply known as the "Bureau of Customs" and the patrol named "U.S. Immigration Service Border Patrol."
The episode takes place on July 30, 1971 when the Apollo 15 moon landing happened, and yet, despite being the dead of summer, all the characters are bundled up and there is snow visible on the ground.
Bernadette gets a letter from US Customs & Border Protection, which didn't exist in the 70s. That letter should have been from the INS which controlled border protection until CBP was established in 2003.
The plot is set in 1971, but the big-rig truck flagged down by Leaphorn is a Mack Super-Liner, a model not introduced until 1977.
The story takes place in 1971, yet the Ford Country Squire wagon stolen from the hospital parking lot by the blonde man has 5 mph bumpers, which means it is a 1973 or later model.