sentences:  It also resides at the transition zone between the subducting Gorda tectonic plate, which is also moving under the North American Plate, the Klamath Mountain Region where the Earth's crust is shortening, and an area of normal faults.In this region, more than 500 volcanic vents have erupted in the past 7 million years.In California, volcanoes like Lassen Peak and Mount Shasta occur among rings of mafic (rich in magnesium and iron) shield volcanoes and volcanic fields such as the Medicine Lake Volcano.