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4 <br />~) <br />Stratigraphy <br />• <br />Jl <br />J~ <br />1' <br />rr~~ <br />1, ~ <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 rtake up the core of the Rocky Mountains. Although these rocks have <br />never been reached by a drill hole 1n, or near, the study area, they are <br />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 />Surrey's designation as "Unnamed Rocks" is deemed appropriate. The Sangre <br />de'Cristo formation of~Pennsytvanian-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 />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 />