Massive Crevasse In California Dam, Country's Largest, Forces Thousands Of Evacuations

OROVILLE, Ca. (CBS) -- A massive crevasse in the nation's largest dam in Northern California has caused hundreds of thousands of people to evacuate, as authorities fear the dam's emergency spillway could collapse.

So far, the immediate threat has subsided.

The California sheriff says repairs on the dam's damaged spillway may be needed before the evacuation is lifted. just as the region braces for more rain.

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Crews in Northern California are trying to figure out whether the spillway at the Oroville Dam and an emergency back-up, can keep rushing water from flooding towns downriver.

Weeks of drenching rain and erosion are testing the spillways connected to the dam, which is the nation's tallest.

The 770 ft., high Oroville Dam is a key part of California's water management, sitting at the head of the Feather River, with Lake Oroville behind it.

Last week, officials noticed a 200 foot-long gash in the dam's main spillway.

On Sunday, water from the rain-swollen lake threatened to overwhelm the eroded emergency spillway, so officials ordered nearly 200,000 residents to evacuate.

"Everybody literally threw everything in their cars and they were gone. It was like a ghost town, walking out into a movie and everybody is gone," said Oroville evacuee Tevin Lee.

For now, water levels at the dam are dropping, taking pressure off the emergency spillway and officials are releasing water through the main spillway to lower the lake's water level before more storms arrive Wednesday.

"I'm a little bit scared," said evacuee Kitty Mastrangelo. ""We're trying not to go near the flooding area so we can go home. But we're probably going to be stuck down here," said Frank Mastrangelo.

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Crews have started loading rocks into bags that helicopters could drop to shore up the damaged spillway.

The entire California National Guard is standing by to be deployed.