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 jntrabasinal 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 CJroup of Pennsylvanian age in the Las Vegas sub-basin is 1,500-2,500 feet thick. These rocks •_-rade 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 subbasin are 900-1,000 feet thick. The terrestrial latest Cretaceous and early Tertiary rocks, which are about 12,000 feet in aL'u'regate 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 t...