Mt. Taylor: Volcanic Necks

Location: mostly 35° 05' to 35° 37' N, 107° 05' to 107° 15' W, Cibola County
Type: Volcanic Necks
Age: Late Pliocene; ~3 Ma to ~2.5 Ma

Vertical erosion through a classic volcanic field; near surface structure of scoria cones and maars


Alkali basalt


The Rio Puerco volcanic necks, including the regionally visible Cabezon Peak, are all part of the Mount Taylor volcanic field. Each neck is a small volcano that erupted during the time that the field was active. The vents are the same age and the original form as those on Mesa Chivato to the west and Mesa Prieta to the east. Landsat image.

Geological Overview

There are few places on Earth where the interiors of young volcanoes are so well exposed as in the Rio Puerco. Cabezon is one of many massive dark peaks known as volcanic necks that are scattered throughout the Rio Puerco valley between Mesa Chivato and Mesa Prieta on the west and east, and San Luis and I-40 on the north and south. Together with Mesas Chivato and Prieta they are part of the Mount Taylor volcanic field, a cluster of several hundred small volcanoes. A few volcanic necks, including Cerro Alesna, occur on the west side of Mesa Chivato. Other examples around the south margin of the Mount Taylor field include half-sectioned volcanoes (east Grants Ridge) and deeply dissected volcanoes (Cubero volcano).

They are all the near-surface interiors of small volcanoes that are geologically young, yet were deeply dissected when the Rio Puerco cut a valley through the Mount Taylor volcanic field. Backwasting of the lava flows and erosion of the volcanoes themselves has exposed the complex interiors of many of the small volcanoes. One may see violent events recorded in their complex structure. The eruptions were similar to those that form small scoria cones, such as Capulin or Bandera volcanoes, and in some cases, similar to that which formed Zuni Salt lake or Kilbourne Hole.


Cabezon Peak. Behind on the right is Cerro Guadalupe, one of the volcanic necks that appears in the USPS New Mexico State Centennial stamp. Beyond in the skyline is the north end of Mesa Chivato, the preserved surface of the Mount Taylor volcanic field. Photo Jayne Aubele


         Cabezon Peak viewed from the west. Photo L. Crumpler


Cerro Alesna is an unusual volcanic neck on the west side of the Mount Taylor volcanic field. Unlike most of the dark and craggy necks in the Rio Puerco valley, Cerro Alesna has huge sweeping massive columns. It consists of an unusual type of volcanic rock, trachyte, benmoreite, or possibly mugearite, rather than the basalt and scoriaceous breccias of the volcanic necks trhoughout the Rio Puerco valley on the east side of the field. The presence of trachyte, benmoreite, and mugearite, rock types that erupt rather viscously and tend to form large lava domes on Mesa Chivato, makes the Mount Taylor volcanic field really unique and rather odd on the North American continent. Photo L. Crumpler


East Grants Ridge (Half section scoria cone).This is an exceptional exposure of the interior of a small scoria cone. And to make the picture easier to see, the cone and its dark scoria sit on top of brilliant white ignimbrites from a nearby earlier rhyolite dome. The massive basaltic "plug" actually narrows down to a small dike only a meter or two wide at the base of the cliff shown here. The whole thing is like something out of a volcanology textbook and is the Grants, New Mexico "Mount Rushmore"! Because it is right next to the paved road in Lobo Canyo, this is also an easy geologic spectacle to visit. Photo L. Crumpler


Basaltic dike exposed in the Mesa Verde Group shales of the Rio Puerco valley. Photo L. Crumpler


New Mexico Centennial Stamp (Santa Clara and Cerro Guadalupe volcanic necks). Contrary to the official description, Cabezon Peak is no where visible in this scene.  The original painting is a serigraph by artist Doug West. 




 Annular Eclipse, May 20, 2012 as seen through peaks on the flank of Cerro Guadalupe. Photo L. Crumpler



Cerro de Santa Clara (the volcanic neck on the left in the State Centennial stamp above) is a classic exposure. Here one can see a feeding basaltic dike approximately 3 to 4 meters wide cutting vertically through tuff breccias probably deposited in a depression during initial explosive opening phases of the volcanic center. Above these are dark basalt lavas that no doubt subsequently filled in the depression. This view is directed north. Photo L. Crumpler


This is an aerial view of essentially the same scene as the photo above. Notice that the volcanic center originally developed without disturbing the pre-exisyting Cretaceous sediments of the Mesa Verde Group. The Rio Puerco snakes its way past at the bottom of the image. Photo L. Crumpler


View the  Mt. Taylor Volcanic Necks in a larger map



All text and photo credit due to Dr. Larry Crumpler, New Mexico Museum of Natural History and Science

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