Inside the desperate battle to shore up the eroded hillside next to Lake Oroville

Evacuees from the Oroville spillway crisis hear the evacuation order being lifted in Bangor. (Brian van der Brug / Los Angeles Times)

Armed with rocks and concrete, officials have been battling to fortify an earthen hillside next to Lake Oroville that has eroded — a critical task in case the reservoir overflows again.

A quarry is being worked around the clock to produce boulders that are being used in a desperate attempt to plug unexpected holes caused by erosion from water overflowing from the lake.

2 3 1 Sources: DWR, Google Earth, detail image courtesy of AFP Getty. Graphics reporting by Rong-Gong Lin II, Chris Megerian, Brian van der Brug and Paige St. John Raoul Rañoa/latimesgraphics Desperate battle to fix emergency spillway Rocks are delivered to a staging area from a quarry. Rocks are carried by dump trucks across the dam and placed in eroded holes in the emergency spillway. Helicopters carry bags of rocks and drop them off on the far side of emergency spillway. Officials are racing to shore up an eroded earthen hillside next to Lake Oroville whose collapse could cause catastrophic flooding if the lake overflows again. Trucks and helicopters are depositing rocks to fill in holes. Emergency spillway Feather River Detailed below Main spillway Oroville Dam Concrete wall Path of water down emergency spillway Main spillway Parking lot and access road flooded when emergency spillway was used Helicopters dump rocks Trucks dump rocks; concrete is poured in eroded holes Lake Oroville Oroville Dam 3000 FT. N 1 3 2