Results of the Field Study of the Surficial Geology and Paleontologic Resources of the Pinon Canyon Maneuver Site, Las Animas County, Colorado

Abstract

Abstract : The Pinon Canyon Maneuver Site contains a large number of fossils and fossil localities, ranging from dinosaur and plant beds to shell beds that were derived in an ancient sea. The lower sequences of sedimentary rocks that are exposed in the canyons along the Purgatoire River were deposited in wind, river, lake and shoreline environments. The upper sequence was deposited in shallow seaway, the Western Interior Sea. The fossils of these marine rocks include clams, snails, and ammonoids that lived in the Gulf Coast region and in other continents. Pinon Canyon is one of the few places in the Western Interior Sea that these species of geographically widespread animals lived. The fossils of the lower canyons include fossil logs that accumulated as log jams the bottom of deep valleys. Nowhere else in the western United States are logs of this age known. Dinosaur bones, dinosaur stomach stones (gastroliths), and plant fossils occur in the Morrison Formation. The upper Dakota Group at the rims of the canyons contain abundant plant fossils, including some of the earliest fossils of flowering plants in the region.