Volcanic Neck, California

Bishop Peak is one of the nine Morros. The Morros are a string of long-extinct volcanoes near San Luis Obispo, in central coastal California, whose magma cores have been exposed by erosion in the 20 million years since they last erupted. The hard rhyolite inside these volcanoes is much more resistant than the soft serpentinite—altered seafloor basalt—that surrounds them. This difference in rock hardness is what lies behind the appearance of volcanic necks. Other examples include Ship Rock and Ragged Top Mountain, both listed among the peaks of the Mountain Western states.