Western Oregon's mountainous regions, home to three of the most prominent mountain peaks of the United States including Mount Hood, were formed by the volcanic activity of the Juan de Fuca Plate, a tectonic plate that poses a continued threat of volcanic activity and earthquakes in the region. The most recent major activity was the 1700 Cascadia earthquake. Washington's Mount St. Helens erupted in 1980, an event visible from northern Oregon and affecting some areas there.