Geology of the Sangre De Cristo Mountains and Adjacent Areas, Between Taos and Raton, New Mexico Kenneth F
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New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/17 Geology of the Sangre de Cristo Mountains and adjacent areas, between Taos and Raton, New Mexico Kenneth F. Clark, 1966, pp. 56-65 in: Taos-Raton-Spanish Peaks Country (New Mexico and Colorado), Northrop, S. A.; Read, C. B.; [eds.], New Mexico Geological Society 17th Annual Fall Field Conference Guidebook, 128 p. This is one of many related papers that were included in the 1966 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. 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CLARK The University of New Mexico; Cornell University INTRODUCTION been subdivided by Clark (1966, p. 16) into a meta- quartzite group, which includes muscovite-hematite gneiss The Sangre de Cristo Mountains of northern New Mex- and granulite, mica quartzite, graphite-mica gneiss, and ico and southern Colorado are a north-trending chain of sillimanite-mica gneiss. Another group with a high con- mountains located between the Rio Grande depression on tent of mafic minerals includes quartz-biotite schist and the west and the Raton basin on the east. These three gneiss, hornblende gneiss, amphibolite, hornblendite, and structural provinces have distinct physiographic expression chlorite schist. The aggregate thickness of these rocks may as indicated in Figure 1. be as much as 10,000 to 12,000 feet. At a later date, intru- The Rio Grande depression in this area is referred to as sion of granites is represented today by pink and gray the Taos Plateau although to the north San Luis basin is varieties of granite and granitic gneiss. In the Moreno more commonly used. Elevations range from approximately Valley large areas of granitic biotite gneiss may represent 7,000 feet at the rim of the Rio Grande Gorge to 8,000 another group of metasediments. feet at the foot of the mountains to the east. In addition The Precambrian granite and granitic gneiss are often the floor of the valley is studded with volcanic cones which associated with zones of migmatites at the contacts with rise as much as 1,000 feet above the surrounding surface. the mafic units. Simple pegmatites are relatively few. In The Sangre de Cristo Mountains, in general terms, can the Taos Range copper mineralization, believed to be of be subdivided into the Taos Range on the west and the Precambrian age, is found in a series of prominent north- Cimarron Range on the east. Separating these ranges lies easterly shears in the Rio Hondo mining district. the high park-like Moreno Valley. The Taos Range in- Precambrian units are to a large extent the result of cludes numerous peaks with summits between 12,000 and regional metamorphism of pre-existing sedimentary and 13,000 feet, in addition to Wheeler Peak, elevation 13,173 igneous rocks, although locally the effects of granitic intru- feet—highest point in New Mexico. In the Cimarron sion are marked. Foliation, in general, is to the northeast Range, altitudes range approximately from 11,000 to 12,500 and is present in most of the rocks to some extent. feet. To the south, the lava-covered Ocate Plateau stands at 9,000 to 10,000 feet above sea level. The floor of the DEVONIAN( ? ) AND MISSISSIPPIAN ROCKS: Moreno Valley is 8,220 feet at the village of Eagle Nest Rocks that have been tentatively assigned to the De- and rises to 8,500 feet and more along its margins with vonian (?) and Mississippian Systems crop out on the the surrounding mountains. mountain peaks and around some of the glacial cirques The Raton basin lies in the western part of the Great west of the Moreno Valley. Isolated exposures of these Plains Province and is hounded by the Cimarron Range rocks are found at Bear Lake, Old Mike, Wheeler Peak, on the west in the vicinity of Ute Park. The plains region Horseshoe Lake, and Lost Lake. In the field the gray lime- consists of the Las Vegas Plateau at elevations between stones contrast sharply with the Precambrian crystalline 6,000 and 6,500 feet, and Raton Mesa, located north of a rocks on which they rest. In the Raton basin these rocks line from Cimarron to Raton, with elevations of 8,000 feet are in the subsurface. Their total aggregate thickness may and more. be 80 feet. The lowest bed consists of a few feet of brown sandstone containing fragments of Precambrian rocks. This is over- STRATIGRAPHY lain by medium- to thin-bedded medium gray limestone A composite table of stratigraphic units with correspond- and dolomitic limestone. The thickness of these beds is ing ages and thicknesses is shown in Figure 2. A brief about 25 feet and they have been assigned to the Espiritu description of the various lithologies is given below to- Santo Formation of Devonian (?) age. gether with other pertinent data. The upper beds consist of a massive ledge of limestone breccia which weathers light gray. This is overlain by sand- PRECAMBRIAN ROCKS: stone, shale, and limestone, some of which may be reddish Precambrian rocks principally occur in the Sangre de or green. The thickness of these beds may be as much as Cristo Mountains, and locally in the Moreno Valley. 40 to 50 feet and they have been correlated with the In this area these metamorphic crystalline rocks have Tererro Formation at the type locality in the Pecos area 58 NEW MEXICO GEOLOGICAL SOCIETY-SEVENTEENTH FIELD CONFERENCE AGE Lithologic Unit Thickness Recent Alluvium, Eolian sand, Mudflow - Pliocene- Pediment gravel - Pleistocene Moraine - Valley fill Basalts - Pliocene High level gravel 135 Monzonite porphyry - Quartz porphyry - Biotite alkali granite - Miocene Hornblende granite - Rhyolite group 1, 360 -1, 500 Latite group 520 Quartz diorite porphyry - Andesite group 1, 500 Paleocene Poison Canyon Formation 2, 500 .----.-1 Raton Formation 1, 700 Vermejo Formation 0 - 550 Trinidad Sandstone 0 - 300 Pierre Shale 2, 300 Smoky Hill Marl 900 Cretaceous Fort Hays Limestone 10- 55 Carlile Shale 165 - 400 Greenhorn Limestone 20 - 60 Graneros Shale 400 Dakota Sandstone 30 - 60 Purgatoire Formation 100 - 150 Morrison Formation 150 - 400 Jurassic Wanakah Formation 30 - 100 Entrada Sandstone 40 - 100 Triassic Dockum Group 0 -1, 200 Permo-Pennsylvanian Sangre de Cristo Formation 5, 300 Pennsylvanian Magdalena Group 5, 000 Mississippian Tererro Formation 40 - 50 Devonian(?) Espiritu Santo Formation 25 Diabas e - Migmatite - Precambrian Granite and granitic gneiss - Mafic gneiss group 7, 000(?) Metaquartzite group 5, 000(?) FIGURE 2 Stratigraphic units in the Sangre de Cristo Mountains and adjacent areas, northern New Mexico. NEW MEXICO GEOLOGICAL SOCIETY-SEVENTEENTH FIELD CONFERENCE 59 (Baltz and Read, 1960, p. 1759 ). There, fossil evidence in- Upper Arkosic Limestone Member is older than that found dicates a Mississippian age for the containing strata. in New Mexico. PENNSYLVANIAN ROCKS: PERMO-PENNSYLVANIAN ROCKS: Pennsylvanian strata assigned to the Magdalena Group Along the western margin of the Moreno Valley and in are found in the western slopes of the Moreno Valley. At the Cimarron Mountains red nonmarine elastic rocks are the crest of the Taos Range, small areas of these rocks re- exposed. They consist of coarse to medium arkosic sand- main either as erosional remnants adjacent glacial cirques stones alternating with thick intervals of siltstone and or are preserved by structural mechanisms. The bulk of shale and a few thin limestones. These materials were de- these sedimentary rocks, however, is poorly exposed in the posited in piedmont alluvial plains. forest-covered mountain slopes and because of this they Locally, this sequence of strata includes gray shale and have been mapped as one unit and not subdivided. These siltstone beds that are carbonaceous and contain speci- marine strata are represented by an alternating sequence mens of Callipteris conferta as well as other fossil plants of conglomerate, medium- to coarse-grained feldspathic that arc indicative of the Permian (?) age of at least the sandstone and arkose, shale, and limestone.