On October 12, 1940, after visiting Pima County Sheriff Ed Echols in Tucson, Arizona, Mix headed north towards Phoenix on U.S. Highway 80 (now Arizona State Route 79), driving his 1937 Cord 812 Phaeton. He stopped to call his agent at the Oracle Junction Inn, a popular gambling and drinking establishment, then continued toward Phoenix. About eighteen miles south of Florence, Mix came upon construction barriers at a bridge washed away by a flash flood. Unable to stop in time, his car swerved twice, then overturned in a gully. A large aluminum suitcase containing money, traveler's checks, and jewels, situated on the package shelf behind his head, hurtled forward and struck him, breaking his neck. He was 60 years old.