This car is clearly a trailer, but was built to be converted to a motor car.  It has the board where a trolley poll would be mounted, but also lacks a hook to hold the pole down.  The PE passenger car suggests the photo dates after the "Great Merger" of 1911, when "old" PE, Los Angeles Interurban, Los Angeles & Redondo, Los Angeles Pacific and other electric railways, in the San Bernardino and Riverside areas merged to form Pacific Electric.  I would guess that this is a former LA&R car.  Trailers were not common but were more common on the LA&R, additionally their shop was adept at building and rebuilding cars, and in the process sometimes creating one off designs.  I suspect that this is not a "Huntington Standard" with two open ends and a closed compartment between, but instead a open/closed car.  The larger open end doesn't match any of the known cars.

Randy Hees