San Felipe volcanic field
San Felipe volcanic field (also known as the Santa Ana Mesa field) is a monogenetic volcanic field located just north of the confluence of the Jemez River and the Rio Grande in New Mexico, US. Description. The volcanic field consists of tholeiitic basalt lava flows, most of which were erupted from fissures and vents aligned from north to south. The largest of these fissures built up the San Felipe shield volcano, which has an elevation of and rises above the base of the lava flows. The flows themselves cover an area of about , which was fairly  flat ground 2.5 million years ago when the eruptions took place. Erosion has since lowered the surrounding terrain and eroded the edges of the field, which now stands as a high mesa, with the basalt cap standing as much as above the Jemez River. In addition to San Felipe volcano, three other major eruption centers and 66 cinder cones have been identified in the field. The cinder cones are aligned close to north-south faults, which show displacements of up to . The cinder cones are unusual in being eroded nearly flat or even appearing as shallow craters on the flow  surfaces. This is attributed to the nearby rivers meandering across the flows after the cinder cones erupted, but before regional uplift raised the field above river level. Some of the cinder cones show ring dikes. Small dikes and plugs are found across the field that are attributed to a late stage of eruption.