Future The High Chaparral (1967) stars Mark Slade and Linda Cristal both appear in this one, but do not share any scenes.
This episode takes place in the 1970s.
A paperback novel, City Under the Sea, authored by Paul W. Fairman, was published in 1965, to tie into the series. Its plot is unrelated to this episode, or to Irwin Allen's later production City Beneath the Sea (1971).