How about an alternate 1980s in which the Cascadia subduction zone experiences a massive earthquake (9.0 is actually not out of the question for the region), resulting in widespread damage and a tsunami along the West Coast. The construction errors and fault line underneath the Trojan Nuclear Power Plant are not discovered in this timeline, so the reactor experiences major core damage. Mt. St. Helens erupts a few days afterwards, releasing ash throughout the region and further stressing the infrastructure of predominately rural Oregon and Washington and complicating relief efforts along the coastline (I don't know about Washington, but coastal Oregon has poor road infrastructure with the rest of the state and no major airports or seaports). The regional fallout may devastate the Northwestern United States and Western Canada, as the fallout may come down in a much more concentrated area due to the massive amounts of volcanic dust in the atmosphere. Also, as discussed earlier, no one really knows how the United States would be able to contain a major nuclear meltdown since the authoritarian methods the Soviets used would be impossible to implement in the United States. Any regional aftershocks would also complicate containment efforts since Trojan was actually built on a faultline, unlike Fukushima.