The Geology and Paleontology of Coglan Buttes, Oregon
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The outcrops of Coglan Buttes in southern Oregon are composed of numerous distinct sedimentary sandstone and volcaniclastic beds. In the past it has been mapped as a single Miocene sedimentary unit. Though the area was known to have produced vertebrate fossils, they had not been studied. My research presented here is the first in-depth study of both the geology and the paleontology of the area. The 620 meters of interbedded sandstones, pyroclastic deposits and volcanic sheet flows change in lateral thickness; they indicate significant paleotopography. In addition I describe the vertebrate assemblages contained within these geologic units and compare them with other North American assemblages. The Coglan Buttes faunas share affinity to those of the John Day Basin assemblages in part, as well as with southern latitude faunas of California, Florida and Texas. The faunal composition of the Coglan Buttes assemblage indicates an earliest Miocene (late Arikareean) age.