Caja del Rio (Spanish: "box of the river") is a dissected plateau, of volcanic origin, which covers approximately of land in northern Santa Fe County, New Mexico, United States. The region is also known as the Caja, Caja del Rio Plateau, and Cerros del Rio. The center of the area is approximately west of Santa Fe, New Mexico. Most of the Caja is owned by the United States Forest Service and managed by the Santa Fe National Forest. Access is through New Mexico Highway 599, Santa Fe County Road 62, and Forest Service Road 24.
Geography
The landscape of the Caja del Rio Plateau is generally flat to rolling terrain, with numerous steep cones rising up to above the plains. The highest points in the immediate area are the unnamed high point , Cerro Micho (), Montoso Peak (), Ortiz Mountain (),Ortiz Mountain is a volcano northwest of Santa Fe, not to be confused with the Ortiz Mountains to the south of Santa Fe. Although shown with an elevation of . on the 1993 Montoso Peak, N. Mex., USGS topographic map, it has been resurveyed at . and Cerro Rito () The entire plateau is within the watershed of the Rio Grande; portions of the Caja drain into the larger river through two tributaries: the Santa Fe River and Cañada Ancha.
Virtually the entire perimeter of the Caja is ringed by cliffs or escarpments. White Rock Canyon forms the northwestern edge of the plateau. This canyon, through which the Rio Grande flows, has a maximum depth of over . Bandelier National Monument lies directly across the river to the west of the plateau. Along the eastern edge is Canada Ancha, an ephemeral stream that flows northward into the Rio Grande near Buckman. Another deep canyon (approximately in depth) runs along the southern edge of the Caja, cut by the Santa Fe River. The canyon of the Santa Fe River separates the Caja land grant from another land grant to the south: the Mesita de Juana Lopez Grant.
At the southern part of the Caja is La Bajada Mesa, dominated by Tetilla Peak (). The western edge of the mesa is a large escarpment known as La Bajada (Spanish: "the descent"), which is easily visible to highway traffic traveling north on Interstate 25 from Albuquerque to Santa Fe. After crossing the Santo Domingo Basin and the reservations of Cochiti and Santo Domingo Pueblo, the freeway makes a steep climb up the escarpment. Further north along La Bajada, at La Bajada Hill, is the site of the old route of El Camino Real de Tierra Adentro, the road from Mexico City to Santa Fe, which was also the original path of Route 66; it involves a tortuous series of 23 switchbacks up the bajada road, which is now closed. La Bajada traditionally forms the southern boundary of the or upper river area of New Mexico, also known as Northern New Mexico.
Geology
The Caja del Rio plateau is a monogenetic volcanic field, which includes approximately 60 cinder cones, spatter cones, and basalt outflows. The volcanism can be explained by the field's location, which is very close to the intersection of the Rio Grande rift and the Jemez Lineament. These structural weaknesses create a thinned crust, and pathways for intrusion by magma originating in the mantle. The result has been a series of intracontinental basaltic eruptions.
The Rio Grande rift is a result of extensional, (or divergent) tectonic forces exerted upon the American Southwest. This feature runs southward from the vicinity of Leadville, Colorado, through the entire state of New Mexico, through the vicinity of El Paso, Texas, and into Chihuahua, Mexico. The rift began forming approximately 30 million years ago during the late Oligocene Epoch.Sawyer, David A., Ralph R. Shroba, Scott A. Minor, and Ren A. Thompson (2002) U.S. Geological Survey Miscellaneous Field Studies Map MF-2352, Geologic Map of the Tetilla Peak Quadrangle, Santa Fe and Sandoval Counties, New Mexico Version 1.0 download The Rio Grande rift takes the form of a series of basins, each offset to the right from the previous basin as one travels along the rift. The Caja del Rio volcanic field lies almost on top of the Bajada Constriction Zone, which is the zone of offset between the Albuquerque Basin to the southwest and the Espanola Basin to the northeast.
The Jemez Lineament is another, older feature, which also represents a linear weakness in the crust. The Lineament trends southwest to northeast, and underlies a string of volcanic features across Arizona and New Mexico. Those features include the San Carlos volcanic field, Springerville volcanic field, Zuni-Bandera volcanic field, Mount Taylor volcanic field, the Jemez volcanic field, the Taos Plateau volcanic field, and the Raton-Clayton volcanic field. The Caja del Rio volcanic field lies in the southeastern part of the Jemez volcanic field.
The lavas erupted in the Caja are diverse in their characteristics, ranging from basalt with a silica content of 49% to dacite with a silica content of 63%. Most are alkali basalts and hawaiites, which are basaltic lavas low in silica and mildly enriched in alkali metal oxides. These originated in the Earth's mantle but mingled with melted crust on their way to the surface. The more silica-rich lavas incorporated more melted crust and are described as evolved magmas. The hawaiites have unusual trace element compositions, suggesting they originated in the remnants of the Farallon plate known to lie below western North America.
Eruptions came in three phases. The first and most voluminous phase lasted from about 2.7 to 2.6 million years ago. The lavas erupted during this phase were mostly basalt and basaltic andesite. Because of their low silica content, these lavas were highly fluid, and spread out to form most of the plateau. The eruptive centers, which included Cerro Montoso, Cerro Colorado, and Tetilla Peak, are mostly large composite cinder cones. The second phase, which lasted from about 2.5 to 2.2 million years ago, was more prolonged but much less voluminous and included a wide range of compositions, including andesite that makes up much of the higher terrain of the Caja del Rio. The final phase, from 1.5 to 1.1 million years ago, was restricted to a small area in lower White Rock Canyon east of the Rio Grande. These flows were basaltic andesite and dacite, and all overlie the lower Bandelier Tuff (Otowi Member) and the youngest overlies the upper Bandelier Tuff (Tsherige Member).
One of the scoria cones of the Caja del Rio, the Cienega volcano (), has been quarried since 1919 for cinder. The quarry has exposed part of the deep plumbing of the volcano, which has been studied for clues to the nature of magmatic plumbing systems under cinder cones. The volcano itself has been radiometrically dated as 2.73 ± 0.06 million years old and erupted through three vents in at least two stages.
Basalt flows on the west side of White Rock Canyon, across from the Caja, are considered geologically part of the Caja del Rio volcanic field. These are mostly composed of tholeiitic basalt, which is similar to the basalt erupted at mid-ocean ridges.
Many of the flows of the Caja del Rio are covered with a mantle of sand, probably originating in the Rio Grande floodplain to the southwest and brought in by prevailing winds.
The Caja is not the only volcanic feature in this part of New Mexico. Approximately to its northwest is the Valles Caldera, a spectacular caldera which lies at the heart of the Jemez Mountains. This mountain range has been created by a series of eruptions since the Miocene. The ages of the first eruptions are difficult to determine, since the older rocks have been almost entirely buried by the material from younger eruptions. The oldest exposed volcanic rocks in the vicinity are approximately 16 million years old. The Jemez area experienced an intense pulse of basalt volcanism between 9 and 11 million years ago. The lavas from this cycle had little silica, and originated in the mantle. Additional pulses of volcanism occurred between 7-10 million years ago, between 6-7 million years ago, between 3-6 million years ago, and between 2-3 million years ago. The last of these pulses is believed to have created the Cerros del Rio volcanic field, which covers the entire Caja del Rio Plateau.
Climate
The climate of the Caja del Rio is arid and continental. The average daily maximum temperature at White Rock, New Mexico varies from in January to in July. The average daily minimum temperature varies from in January to 54.4 degrees in July. That average annual maximum temperature is , with the average annual minimum at . The average annual precipitation is approximately -. Most of the annual precipitation is associated with summer thunderstorms, although the area also receives winter snow.
Ecology
Soils in the Caja del Rio are derived from Tertiary volcanic basalt flows and cinder cone eruptions. Most are best characterized as stony or cindery loam, with shallow horizons. Soil surveys of the Caja generally describe the soils as unsatisfactory, with a reduced potential for hydrologic and nutrient function.
Three primary plant communities are frequently found on the Caja del Rio plateau: pinon-juniper savanna, pinon-juniper woodland, and Great Basin sage scrub. The most prevalent vegetative communities consist of a pinon (Pinus edulis) and juniper (Juniperus monosperma) overstory with a short grass understory. Tree densities often range between 100 and 300 trees per . Another large community consists of open grassland, with blue grama (Bouteloua gracilis), galleta (Pleuraphis jamesii), and various species of Stipa being the most common grasses. Common woody shrubs include chamisa (Chrysothamnus nauseosus), Apache plume (Fallugia paradoxa), four-wing saltbush (Atriplex canescens), and big sagebrush (Artemisia tridentata).
Predatory mammals known to live in the Caja del Rio include black bear (Ursus americanus), mountain lion (Felis concolor), bobcat (Lynx rufus), coyote (Canis latrans), fox (Vulpes spp.), gray fox (Urocyon cinereoargenteus), ringtail (Bassariscus astutus), badger (Taxidea taxus), long-tailed weasel (Mustela frenata), western spotted skunk (Spilogale gracilis), and striped skunk (Mephitis mephitis). Non-predatory mammals known to be present include Rocky Mountain elk (Cervus elaphus), mule deer (Odocoileus hemionus), raccoon (Procyon lotor), porcupine (Erethizon dorsatum), black-tailed jackrabbit (Lepus californicus), desert cottontail, (Sylvilagus auduboni), white-throated woodrat (Neotoma albigula), Botta's pocket gopher (Thomomys bottae), Colorado chipmunk (Neotamias quadrivittatus), pinyon mouse (Peromyscus truei), and deer mouse (Peromyscus spp.). Sensitive mammalian species known to be present at the Caja include Gunnison's prairie dog (Cynomys gunnisoni). A small herd of wild horses (consisting of approximately 50 individuals) lives year round on the plateau.
Birds of prey found in or near the Caja include bald eagle (Haliaeetus leucocephalus), golden eagle (Aquila chrysaetos), red-tailed hawk (Buteo jamaicensis), ferruginous hawk (Buteo regalis), Swainson's hawk (Buteo swainsonii), American kestrel (Falco sparverius), and peregrine falcon (Falco peregrinus anatum). Other resident non-migratory birds include Merriam's turkey (Meleagris gallopavo), pinyon jay (Gymnorhinus cyanocephalus), hairy woodpecker (Picoides villosus), and scaled quail (Callipepla squamata).