Mahoney was cast as an engineer, Andy Prentis, in the 1954 episode, "Husband Pro-Tem," on the syndicated anthology series, "Death Valley Days", hosted by Stanley Andrews. In the story line, Prentis is hired by a railroad executive, Alonzo Phelps (Howard Negley) (1898–1983) to negotiate a private agreement with the Indian Chief Black Hawk (Lane Bradford) so that a railroad can be constructed across Indian lands. In his assignment, Prentis soon romantically tangles with Phelps' daughter, Evelyn (Gloria Marshall) In February 1956, Mahoney co-starred with his wife Margaret Field in the Death Valley Days episode "Swamper Ike".