Hauling field gear up Gothic Mountain…
ABSTRACT Raton Basin.—The Raton basin of northeastern New Mexico and southeastern Colorado is a Laramide structural basin bounded on the west by the Sangre de Cristo uplift, on the north by the Wet Mountains uplift and Apishapa arch, and on the east by the Sierra Grande arch. The basin is asymmetrical and the northerly trending axis generally is near the Sangre de Cristo uplift. The intrabasinal Cimarron arch separates the structurally deeper northern part of the Raton basin from the shallower, southern, Las Vegas sub-basin. During most of Paleozoic time the Raton basin and its bounding uplifts were part of the relatively stable “continental backbone.” The oldest known sedimentary rocks in the basin are marine beds of Devonian(?) and Mississippian age. In Early Pennsylvanian time the Rowe-Mora and Central Colorado geosynclinal basins were formed in the area of the present Sangre de Cristo uplift and the western half of the present Raton basin. The basins were bounded on the west by the intermittently rising San Luis uplift, and on the east and north by the ancestral Sierra Grande, Apishapa, and Wet Mountains uplifts. A mainly marine unstable shelf facies of the Magdalena Group of Pennsylvanian age in the Las Vegas sub-basin is 1,500-2,500 feet thick. These rocks grade abruptly northward into a marine geosynclinal facies which is as much as 6,000 feet thick in the Las Vegas sub-basin. The Magdalena Group is absent from the Cimarron arch, but it probably is present in the western half of the northern Raton basin where it may be 4,000 feet thick. Orogenic debris of the Sangre de Cristo Formation of Pennsylvanian and Early Permian age was derived mainly from the San Luis uplift, filled the Rowe-Mora and Central Colorado basins, and lapped onto Precambrian rocks of the other bounding uplifts. The Sangre de Cristo Formation is 700-3,500 feet thick at the south, and 6,000-9,500 feet thick at the north. Higher Permian rocks, and Upper Triassic and Upper Jurassic rocks have average aggregate thicknesses ranging from 2,300 feet at the south to 1,100 feet at the north. These deposits blanketed the region of the present Raton basin and buried the late Paleozoic, Sierra Grande, and Apishapa uplifts. Cretaceous marine shale interbedded with some sandstone blanketed the entire region. The Cretaceous rocks are about 4,500 feet thick at the north, and remnants in the Las Vegas sub-basin are 900-1,000 feet thick. The terrestrial latest Cretaceous and early Tertiary rocks, which are about 12,000 feet in aggregate maximum thickness in the northern part of the Raton basin, were derived mainly from the rejuvenated San Luis uplift. During early and middle Tertiary time, the San Luis uplift and the western parts of the Paleozoic Rowe-Mora and Central Colorado basins were elevated to form the Sangre de Cristo uplift. The present Raton basin, Wet Mountains uplift, and the Apishapa, Las Animas, and Sierra Grande arches were formed in early Tertiary time. The Raton basin has been a basinal area for most of its history since Early Pennsylvanian time. Thick marine sediments of Pennsylvanian and Cretaceous ages probably were sources of petroleum. Potential traps, both stratigraphic and structural, are known to exist in many parts of the basin, although these traps are mainly untested. Encouraging “shows” of oil and gas have been found in Pennsylvanian rocks in the Las Vegas sub-basin, and in Cretaceous rocks in several parts of the basin, but there has been no commercial production. San Luis Basin.—In middle and late Tertiary time the ancient San Luis uplift was tilted eastward and its eastern part foundered to form the San Luis basin, which is the northern part of the complex Rio Grande trough. The northwestern part of the San Luis basin merges into the eastern flank of the San Juan Mountains uplift. The southwestern part of the basin is bounded by the east-tilted Brazos uplift. The eastern and northern boundaries of the basin are a complex fault zone along the western margin of the Sangre de Cristo uplift which merges, around the northern end of the basin, with the Sawatch and Gunnison uplifts. Much of the San Luis basin is filled with middle to upper Tertiary and Quaternary terrestrial sediments and interbedded andesite and basalt that are at least 5,000 feet thick locally. This basin fill rests on lower and middle Tertiary volcanics that are related to the volcanics of the San Juan Mountains. Because the region of the San Luis basin was a part of the Paleozoic and Mesozoic San Luis uplift, it is doubtful that extensive areas of Paleozoic or Mesozoic rocks are preserved beneath the lower to middle Tertiary volcanics. The stratigraphy and geologic history of the San Luis basin are not encouraging for petroleum possibilities.
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