Could not have been erosion from the top because the dam was not close to full. Water made its way through the earthen fill dam and cavitated some hellacious holes pronto.
Art....the water would never have flowed out of the emergency spillway if the lake weren't full...and the lake would have never completely filled if the DWR people hadn't cut the flow back on the main spillway from the 90K + CFS they were releasing prior to the decision to cut the flow and try out the emergency spillway. On top of it all, I seriously doubt the "EMERGENCY" spillway was designed to operate with the main spillway gates over half way closed.
