Colton Crater is a large cinder cone in the central part of the San Francisco volcanic field, just south of the more well known SP Crater. At some point near the end of its eruptive live, the vent underwent a major phreatomagmatic (groundwater-magma interaction) event that blew out the central core of the cone and fueled pyroclastic surges that raced over the crater rim. This resulted in deposits of palagontized tuff that mantle the north rim. From rim-to-rim the crater maw (E-W and N-S) is about 0.70 miles.
The xenolith-rich tuff includes bits and pieces of older basalts, Coconino Sandstone and Kaibab Limestone, and pyroxene megacrysts that may have originated at magma chambers at the crust-mantle boundary.
Following the phreatomagmatic blast(s), the eruptive style returned to the common Strombolian style characteristic of cinder cones producing the small cinder cone at the center of the crater interior. (Aerial photo by pilot Ted Grussing.)