This series of photographs appear to have been shot during 1931-2 during construction.
There are some details of interest if one wishes to look closely.
1. Note the period streetlights similar to the Gothic Revival style of the 4th Street Viaduct directly upstream.
These have long been replaced by the ubiquitous "cobra head" lights which lack style but are much more efficient.
2. The photographer is unknown and uncredited; the photos are from the LA City Library archives and are presented here as large as possible.
I have photoshopped them to reveal as much detail as possible, however I have not tried to remove the damage seen in the negatives.