Judging from the tools displayed, likely a Beta Chapter work party.
Photo from the Archives of The Museum of the San Fernando Valley 1013-002-6318
Among slides found by Jerry Fecht 2013 / Processed by Gary Fredburg(Click on the image to enlarge it, or to display it fully)
(l to r front row) Missing or unsure names are indicated by number.
Frank Demarco, (2), (3), LeRoy Hunt, Tom Shanley and Jim Reeves
(l to r top row)
Bob Robar, Larry Tunison ??, (4) sunglasses (5), (6) and Don Collins