Standing alone in north-central California, the stratovolcano known as Mount Shasta dominates the skyline and can be seen from over 100 miles (161 km) away. At 14,179 feet (4322 m) this peak is the second-highest in the volcanic Cascade Range, only 232 feet shorter than Mount Rainier in Washington. Made up of four overlapping cones of varying age, this volcano began its life about 600,000 years ago with its first eruption. The most recent eruption was in 1786 and was observed by sailors in the nearby Pacific Ocean.
Mount Shasta is only one of many large volcanoes found throughout the Cascade Range from northern California to British Columbia. All of them have been formed by the same basic geologic process. For the last few millions of years the North American tectonic plate has slowly overridden the Juan de Fuca plate to the west. As the lighter continental crust has sunk the denser oceanic crust beneath it, the ocean crust has gradually melted and risen to the surface of the overlying continent. All of this ascending molten rock has lead to a chain of composite volcanoes along the margin, creating today’s Cascade Range.
The prominent volcano just to the right of Mount Shasta is Mount Shastina. Formed earlier than Shasta, this mountain is 12,300 feet (3760 m) in height and alone ranks as the fourth-highest peak in the Cascades. Shasta itself is still potentially active and may present a threat to the scattered population centers of northern California.