According to the caption
on the back of the original photo (and according to Brunner's 1940 history, which includes a copy), this image was
"Taken March 9, 1928, by E.B. (Al) Louden." It's one of at least three known images Louden shot at the dam that day.
Louden (or someone at the time) mass-produced this image as souvenir after the dam broke. It appears in a number of collections. One version in the SCV Historical
Society collection — probably Brunner's copy — says: "Walking the parapet are William Mulholland, Harvey Van Norman and Tony Harnischfeger" (misspelled "Harnischferger").
This was thought to be the last photograph of the St. Francis Dam "intact," until this one turned up.
Also, there is a local urban legend that says this photograph was shot at noon on March 12, 1928. It wasn't.
HS2808: 2400 dpi jpeg from original print. Same as HS7036, SCV Historical Society collection.