The San Andreas fault is the border between two tectonic plates—the North American Plate and Pacific Plate. Los Angeles is located on the Pacific Plate, and San Francisco is on the North American Plate. In a few million years, the two geographic areas will be right next to each other because the western side of the fault (the Pacific Plate) is moving northward with respect to the rest of the state. The fault is moving at about 2 centimeters (just under an inch) per year.
The massive magnitude-9.2 Alaska earthquake changed the world by proving plate tectonics works. Since the quake struck on March 27, 1964, there has never been another earthquake as powerful. The remarkably low death toll of 131 people belies the quake's incredible effects on the Earth.
Plate/Plate Boundary that created Volcano: Mt. Redoubt was created by a convergent continental/oceanic plate boundary. Picture: Diagram showing the North American and Pacific plates converging while the Pacific plate is subducting beneath the North American plate. Picture Source: http://www.nps.gov/lacl/naturescience/volcanoes.htm
For 80 million years, a volcanic hot spot on the Pacific Plate has been releasing lava that has piled up as volcanic rock to form the Hawaiian Islands.