Mount St. Helens' eruption in 1980 primarily affected cities and towns in Washington State, particularly those located to the north, east, and south of the volcano. Here are some of the most significantly impacted areas:

* Spirit Lake: The lake was completely filled with volcanic debris, burying the surrounding forest.

* Toutle River Valley: The eruption caused a massive landslide and mudflow that devastated the Toutle River valley, damaging bridges, roads, and homes.

* Longview, Washington: This city, located about 50 miles southwest of Mount St. Helens, was heavily affected by the ashfall, which caused significant disruption to transportation, power, and communication systems.

* Vancouver, Washington: Located about 40 miles southwest of the volcano, Vancouver also experienced significant ashfall and disruption.

* Portland, Oregon: Although further away, Portland experienced significant ashfall and disruption to air travel and other transportation systems.

It's important to note that the impact of Mount St. Helens' eruption extended beyond these specific cities and towns. The ashfall affected a wide area, impacting agriculture, transportation, and the environment in many parts of the Pacific Northwest.