What action did the partially completed Oroville Dam take in 1964?

The action taken by the partially completed Oroville Dam in 1964 that is most notable is that it saved the Sacramento Valley from flooding. At the time, the dam was not fully operational, but it was able to hold back significant floodwaters resulting from heavy rainfall and runoff. This flood control function was crucial for protecting the surrounding communities and agricultural lands in the valley, highlighting the dam's role in flood management even in its incomplete state.

Other options do not accurately reflect the main contribution of the Oroville Dam during that period. Improvements in irrigation methods would be more related to water management practices rather than the actions of an incomplete dam. While providing drinking water for Los Angeles or facilitating hydroelectric power generation are important roles of the Oroville Dam, those functions were not realized until it was fully completed and operational after 1968. The dam's capacity to mitigate floods was a critical immediate benefit, especially given the frequent flood risks associated with California's winter storms.