Geology of the Las Vegas area
We document a rich Upper Triassic bonebed in Borden County, Texas in either the uppermost Tecovas Formation or, more likely, the Trujillo Formation of the Chinle Group, that represents one of the highest stratigraphic occurrences of the aberrant archosauromorph reptile Trilophosaurus. The associated fauna includes indeterminate coprolites, unionid bivalves, osteichthyans, indeterminate reptiles, a possible ornithischian dinosaur, and the putative theropod dinosaur Spinosuchus caseanus Huene.
Geologic-Climatic Dating in the West
Geologic-Climatic dating of archaeological finds in the arid and semiarid western United States is based on geology, on the relationship between moisture, vegetation, and geological processes, and on climatic history. The procedure of dating includes 4 main steps, namely, (1) study of beds and geological features, (2) climatic interpretation of beds and features, (3) assignment of the bed with the human record to a particular regional climatic age or phase, and (4) correlation of the regional relative chronology with a dated climatic history. The geological study of the site includes texture, structure, and appearance of the beds or terrace deposits, their modes and conditions of formation, their sequence, fossils, and artifacts, the soil zones, caliche incrustations, and erosions. The climatic interpretation of the beds and features is made in conformity with the delicate regional relationship between climatic conditions and changes and geological processes and deposits.
Patterns and Origin of Radial Dike Swarms Associated with West Spanish Peak and Dike Mountain, South-Central Colorado
West Spanish Peak and Dike Mountain in south-central Colorado are stocks which cut Tertiary sedimentary rocks near the axis of the La Veta syncline, the structural trough of the Raton basin. Associated with these stocks are radial dike swarms. The outline of the West Spanish Peak dike swarm is elliptical. The Dike Mountain swarm is more radial, and its outline is oval. Both systems are elongated normal to the axis of the La Veta syncline. The dikes of the West Spanish Peak swarm are of diverse rock types and represent several separate magmatic phases. Those of the Dike Mountain swarm are facies of syenodiorite and probably represent a single phase of magmatic invasion. The dikes occupy vertical joints that have been generally attributed to radial fissuring during doming of the sedimentary rocks by the emplacement of the stocks. Structural studies, however, indicate that several systems of shear and tension joints resulted from intermittent orogenic stresses of varying direction and magnitude during folding of the syncline before invasion of the magmas, and the writer suggests that selective intrusion into this joint complex accounts for the dike patterns.