Photo by: Frank D. Robinson - Merced; L.A.Foster Collection Courtesy of Donald Foster Caption lettered on photograph: "#8 Bridge No. 3 Y.V.R.R. Relocation Loading Holes Pier No. 6 Davis Heller & Pierce contr's 5/1/25" In other words these four "Power Monkeys" are setting dynamite charges - packed in deep holes. They used the long rods they holding to push the charges into the holes and to pack "Mud" over the dynamite. Without the "Mud" packing the blast would only blow through the hole with no real effect.