State and local officials are required by the /*Federal Energy Regulatory Commission*/ to test an emergency action plan.
The exercise simulated an imminent failure of the dam caused by an earthquake.
A collapse of the Oroville Dam could flood more than one million acres in eight Northern California counties.
Oroville Dam holds back /*Lake Oroville*/, the main reservoir of the state water project system.
When full, Oroville has enough water to supply about 40 percent of the state's urban water needs for a year.