The Cerros del Rio Volcanic Field is one of many volcanic fields in northern New Mexico. It lies within the Rio Grande rift and has been cutt by the Rio Grande. The cayon that resulted, White Riock Canyon, was too steep, rocky, and narrow foir early travelrs. Hence early colonist were forced up and over the land south and easts of the Cerros del Rio volcanic field much as Interstate Highway 25 does today.
" The Santa Fe Volcanic Field" (or so it should be named)
The Cerros del Rio Volcanic Field lies on the western edge of Santa Fe and between Santa Fe and the Rio Grande/White Rock Canyon. In fact the Cerros del Rio forms the western skyline for the entire city. Many small volcanic cones are visible toward the west on any given evening. From the Museum Hill on the southeastern edge of Santa Fe, there is an excelllent view of both the Cerros del Rio and the Valles Caldera beyond.
View west from Museum Hill, Santa Fe. Ironically, few Santa Feans realize that they live right next door to and can see from their windows the site of one of North America's latest super eruptions, the Valles Cadera. Photo L. Crumpler
The Rio Grande naturally sections the Cerros del Rio field creating White Rock Canyon. Like much of New Mexico's volcanic record, surface erosion is minimal, but vertical dissection can result in unusual natural cross sections. IN the case of White Rock Canyon ddown-cutting bt the Rio Grande exposes a variety of lava flow sections and phreatomagmatic deposits. View directed northward along White Rock Canyon. Buckman Mesa on the far right distance.
Montoso maar is an unusual exposure created when a side canyon off of White Rock Canyon emncroached through the center of a maar. As a result, one can stand on the deposits of blocks and ash forming the crater rim, yet descend into exposures of the upper one hundred meters of the same maar by walking down the canyons.
Schematic cross section of Montoso maar. Some of the tuff breccias within the lower crater floor are spectacularly exposed along the canyon walls.
Columnar joints in an intrusion in the floor of the Montoso maar.
Section exposing blocks of sedimentary country rock caught in the debris of the lower inner maar walls.
View of the southern margin of the Cerros del Rio field, La Bajada escarpment and I-25. On the left horizon is the rim of the Valles Caldera. On the right distance is the profuile of the Cerros del Rio field.
The Ceja Box or Buckman Mesa road area is a section of ponded lava flows a couple of hundred feet thick at the northern end of the Cerros del Rio Volcanic Field. It is a famous locality for some movies. Here a major arroyo cuts trhough the volcanic field and enters the Rio Grande, cutting a beautiful section of the field.
Inward-dipping aglomerates rin the summit structural crater of Cerro Colorado, one of the larger scoria cones in the Cerros del Rio field. The field is an extensive "forest"of piñons and junipers.
Scoria on one of the cones is encrusted with specular hematite. It seems that in every volcanic field there is at least one cone or volcanic dome where specular hematite occurs.
At the south end of the volcanic field, not far from the Santa Fe airport, there is an area of ash-covered camel tracks. The dark scoria in the background post-dates the tracks, so these are the tracks of a camel that passed through around 3 million years ago, probably in the damp ash fall materials of a nearby maar.
Geological Overview of Volcanism
The volcanic field represents the younger of a series of three extended time period over which mafic volcanism pre-date the silicic eruptions leading up to Valles Caldera formation. ranging from alkali basalt to andesite. Most of the eruptive volume occurred the 2.3-3.2 (Baldrige, 2004). Eruptions consisted of alakli basalts and transition high alkali intermediate or andesitic compositions. Andesitic eruptions are relatively low in volatiles such that flows are thick and originate from vents with very small pyroclastic centers. The volcanic rocks thicken towards the Rio Grande implying that the volcanism was contemporaneous with downcutting of the river through the accumulating volcanoclastic sediments. Maars, originally identified during mapping of the field, are common, including a half-sectioned example (Montoso maar).
Geologic Map of the Cerros del Rio field, J.C. Aubele, 1978
Frijoles Canyon on the west side of the Rio Grande at White Rock Canyon cuts through a sequence of massive phreatomagmatic and volcanoclastic deposits.
View Cerros del Rio volcanic field in a larger map
Aubele, J. C., 1978, Geology of Cerros del Rio volcanic field; in Hawley, J. W. (ed) Guidebook to Rio Grande rift in New Mexico and Colorado: New Mexico Bureau of Mines and Mineral Resources Circular 163, p. 198-201.
Aubele, J. C., 1979, The Cerros del Rio volcanic field: New Mexico Geological Society 30th Field Conference Guidebook, p. 243-252.
Aubele, J. C., 1999, Cerros del Rio volcanic field: New Mexico Geological Society 50th Field Conference Guidebook, Albuquerque Geology, p.13-14.
Dethier, D. P., 1989, Geology of White Rock quadrangle, Santa Fe and Los Alamos Counties, New Mexico: New Mexico Bureau of Mines and Mineral Resources Map, 1:24000 scale.
Duncker, K. E., 1988, Trace element geo-chemistry and stable isotope constraints on the petrogenesis of Cerros del Rio lavas, Jemez Mountains, New Mexico [M.S. thesis]: University of Texas, Arlington, 158 pp.
Manley, K., and Mehnert, H. H., 1981, New K- Ar ages for Miocene and Pliocene volcanic rocks in northwestern Espanola basin and their relationship to the history of the Rio Grande rift: Isochron/West, no. 30, p. 5-8.
Zimmerman, C., and Kudo, A. M., 1979, Geology and petrology of Tetilla Peak, Santa Fe County, New Mexico: New Mexico Geological Society 30th Field Conference Guidebook, p. 253-256.