The Grand Coulee Dam in the Columbia River Basin in Washington has a ginormous capacity of 6.8 GW, making it the 6th largest power plant in the world and the biggest producer of power in the US. It has a greater capacity than any nuclear, coal, or gas plant anywhere. In total, the Columbia River Basin generates a whopping 44% of all hydro power in the U.S.
Hydro accounts for 8 of the top 10 power plants in the world, the other two are nuclear. The Grand Coulee Dam is the only US power plant in the top twenty worldwide.
A significant amount of hydroelectric power generated in the Northwest is consumed by California customers. In the late 1960s, BPA constructed two 500-kilovolt transmission lines capable of carrying power from the Pacific Northwest to the Los Angeles area. The Pacific Northwest-Southwest intertie was completed in 1971, giving Los Angeles consumers access to hydroelectric power originating from the Pacific Northwest.
Big hydro is not considered renewable energy in California. Small hydro is. Large dams can create enormous environmental damage, including erosion, and can contribute to earthquakes because of their enormous weight.