Liz wins with her 2:56 p.m. Tuesday guess "on the east side of the San Rafael ave bridge...casting balustrades"
In the photo above, an unidentified worker stands with cast iron baluster molds in 1922 near the San Rafael Bridge in Pasadena, which was under construction.
The original photo is on page 16 of the San Rafael Bridge photo scrapbook in the Centennial Room at Pasadena Central Library.
Here's an early construction photo:

And the bridge today:

If you've never been on the San Rafael Bridge, it's the southernmost bridge over the Arroyo Seco in Pasadena. You can access it from South Arroyo Boulevard and from South San Rafael Avenue.
San Rafael Bridge is one of the contributing resources of the Arroyo Seco Parks and Recreation Historic District, which is on the National Register of Historic Places. Others among the 14 contributing resources include Brookside Golf Club, Rose Bowl Stadium, Brookside Park, Holly Street Bridge, Colorado Street Bridge, Mayberry/Parker Bridge, La Casita del Arroyo, Lower Arroyo Seco Park and the Bird Sanctuary.