The subduction zone has existed for at least 37 million years, and has created a line of volcanoes called the Cascade Volcanic Arc which stretches over along the subduction zone. Several volcanoes in the arc are potentially active. Lassen Peak in California, which last erupted in 1921, is the southernmost historically active volcano in the arc, while the Mount Meager massif, just north of Mount Garibaldi, which erupted about 2,350 years ago, is generally considered the northernmost. A few isolated volcanic centres northwest of the Mount Meager massif, such as the Silverthrone Caldera, which is a circular wide, deeply dissected caldera complex, are considered by some geologists to be the northernmost member of the arc.