Colton Crater is a large cinder cone in the central part of the San Francisco volcanic field. At some point near the end of its eruptive live, it underwent a major phreatomagmatic (groundwater-magma interaction) event that blew out the central core of the cone and fueled pyroclastic surges racing over the crater rim. The latter resulted in deposits of palagontized tuff mantling the north rim.
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.