James Bridges wrote parts of the China Syndrome, Urban Cowboy and other films on a manual Underwood typewriter in a relatively cramped, windowless studio office in the basement of the Sturges house. Since the main floor is so small, Bridges must have felt a need to "hide out" below (a somewhat curious choice given the huge primary deck and expansive roof deck, but certainly a place to get away and focus).
Debbie Getlin, Bridges long-time assistant recounts that he would wake up at 5am, draft a series of pages on his Underwood and leave them for her on the Lautner dining table, where she would plug-in and retype on her electric typewriter.
Without a doubt, Wright didn't contemplate the basement as finished space. Tucked under and accessed by a narrow stair, the basement is primarily an artifact of the prodigious cantilver. And the basement was an extremely unusual feature in a Los Angeles house of the era.
That said, the basement has a surprising charm. Briges also used the basement as a dark room to develop film.