The cinder cone we know as Capulin Volcano serves as the centerpiece for an amazing display of volcanic features in and around the national monument. It shares the landscape with hundreds of other cinder cones and basaltic lava flows, rhyolitic volcanic domes and a large andesitic shield volcano. This volcanic field includes lavas of wide chemical range: from rhyolite (> 68 weight % SiO2), to dacite (63-68 wt % SiO2), to basalt (< 52 wt % SiO2), as well as varieties of these end-member compositions. 

Beginning in the Cretaceous Period, about 146 to 65 million years ago (Ma), prior to the volcanic eruptions in the area that would become northeastern New Mexico, this region was covered by an interior seaway that initially connected the Arctic Ocean and the Gulf of Mexico. This seaway expanded and contracted throughout the Cretaceous. When it expanded, dark-colored, fine-grained marine sediments were deposited, such as the Pierre Shale, which can be seen in outcrop along Interstate 25 between Las Vegas and Raton.

When the seaway contracted, beach, river, and delta deposits covered the marine sediments. As the Rocky Mountain Range began to rise, this seaway retreated forever.

Beginning about 9 million years ago, in the western region that is bounded today by the New Mexico towns of Raton and Clayton, called the Raton-Clayton Volcanic Field (RCVF), large volumes of lava were erupted onto either the Ogallala Formation (Miocene age) or the Poison Canyon Formation (Paleocene age). The Ogallala Formation was formed from the deposition of sediment carried by rivers from the Sangre de Cristo Mountains, and today serves as a major source of groundwater for much of the Great Plains. These lavas also erupted on the northern and southern perimeters of the RCVF. Chemically the majority of the lavas erupted during this time are classified as either olivine basalts or alkali basalts. Another type of lava erupted here is the Red Mountain rhyodacite, which erupted between 6.8 and 6.3 Ma; this lava comprises Red Mountain, a rhyolitic volcanic dome, on Johnson Mesa. These lavas are grouped together in what is referred to as the “Raton Phase” of RCVF activity.

The next phase of volcanic activity began approximately 3.0 Ma at Rabbit Ears, which today is an eroded vent near Clayton, New Mexico. This stage of volcanism is referred to as the “Clayton Phase” as the majority of lavas erupted during this time are found between Clayton and Sierra Grande; although, Jose Butte and Robinson Peak are located west of Capulin.  The Clayton lavas typically have very low SiO2 content (42-45 wt %) and are classified as nephelinite and basanite. 

The Capulin Phase lavas were also erupted onto the Ogallala Formation, as well as onto the light-brown sandstone called the Dakota Sandstone (Cretaceous Age), which locally crops out near the towns of Folsom and Des Moines.

Presently, there is no evidence to suggest that the volcanism in this phase has ended, and it may only be in an eruptive hiatus. However, since the last known eruption occurred more than 30,000 years ago, the RCVF is considered dormant.