Thanks ProphetM, I completely forgot about the third stairway...
Google Street View
...and may have inadvertently (stupidly) cropped it out. Do you think this may be it?
http://digitallibrary.usc.edu/cdm/co.../17705/rec/262
All three here:
http://digitallibrary.usc.edu/cdm/co.../17705/rec/262