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4 <br /> Stratigraphy <br /> Rocks exposed in the region range in age from Precambrian to Quater- <br /> nary and are described by Wood, et al . , 1957; Johnson, 1961 ; Pilmore, 1969; <br /> and Levings, 1951 . Although only the Raton formation and Quarternary de- <br /> posits are exposed in the study area, the entire stratigraphic section will <br /> be briefly described here. <br /> The oldest rocks of the region are the Precambrian crystallines that <br /> also make up the core of the Rocky Mountains. Although these rocks have <br /> never been reached by a drill hole in, or near, the study area, they are <br /> j thought to be over 15,000 feet below the surface and are thought to be <br /> similar to the granites, gneisses, schists and quartzites that are exposed <br /> in the Sangre de Cristo Mountains a few miles to the west. <br /> Information concerning Paleozoic systems of rock comes from outcrops <br /> in'the Sangre de Cristo Mountains and from drilling outside the study area. <br /> The oldest sedimentary rocks are Pennsylvanian in age and estimated at ap- <br /> proximately 3500 feet in thickness. They consist of sandstones, shale and <br /> limestones. There appears to be little consistency in the usage of forma- <br /> tional nomenclature for the Pennsylvanian rocks, and the Colorado Geological <br /> Survey' s designation as "Unnamed Rocks" is deemed appropriate. The Sangre <br /> de Cristo formation of Pennsylvanian-Permian age consists of conglomerates, <br /> sandstones, shales and nonmarine limestone. Its thickness in the study <br /> area is unknown, but based on interpolation between areas to the west and <br /> southeast, it is estimated at approximately 10,000 feet. <br /> i <br /> The Ocate formation, a Jurassic sandstone 30-65 feet thick overlies the <br /> Sangre de Cristo formation. The Ocate is overlain by 15 to 40 feet of <br /> shale with interbedded sandstone and limestone assigned to the Wanakah(?) forma- <br /> tion by some workers. Uppermost Jurassic is represented by the Morrison <br /> formation. It consists of thick beds of gray, green, red, brown and varie- <br /> gated claystone and siltstone along with thin beds of sandstone and lime- <br /> stone. Thickness of the Morrison, estimated from neighboring areas, is 250 <br /> to 300 feet. <br /> The lowest Cretaceous unit is the Purgatoire formation, a conglomeratic, <br />