High-resolution seismic images of lithospheric structures allow us to infer the tectonics that modified the lithosphere. We apply such methods to understand Cenozoic modification of the lithosphere by tectonic and magmatic processes in the tectonically active western United States. Using USArray Transportable and Flexible Array data, we present high-resolution images for three regions in this thesis. (1) In the Mendocino triple junction, we use a joint inversion of Rayleigh-wave dispersion data and receiver functions to obtain a new crust and upper Vs model to ~150km depth. The model shows four distinct, young lithosphere-asthenosphere boundary systems. A low-Vs anomaly beneath the Great Valley-Sierra Nevada reconciles existing slab window models with the mantle-wedge geochemical signatures in Coast Range volcanics, and explains the ~3 Myr delay of the onset of volcanism after slab removal. Uppermost mantle low velocities provide evidence for forearc mantle serpentinization extending along the Cascadia margin. (2) In the Colorado Plateau, a Rayleigh wave tomography model sheds light on the volcanism along the margins and plateau uplift. Strong upper mantle heterogeneity across the plateau edge results from the combined effect of a ~200-400 K temperature difference and ~1% partial melt. A ring of low velocities under the plateau periphery suggests that the rehydrated Proterozoic lithosphere is progressively removed by convective processes. Particularly, a high-Vs anomaly imaged beneath the western plateau adds evidence for a downwelling/delamination hypothesis [Levander et al., 2011]. Thermo-chemical edge-driven convection causing localized lithospheric downwelling provides uplift along the margins and magmatic encroachment into the plateau center. (3) In the final study, we developed a 3-D teleseismic scattering wave imaging technique based on the Kirchhoff approximation and 3-D inverse Generalized Radon Transform. Synthetic tests demonstrate higher resolution imaging for continuous, irregular interfaces or localized scatterers, in comparison to conventional methods. Applied to the High Lava Plains dataset, the transmission coefficient structure shows a deepening Moho near 117.6°W and three negative events that correlate well with the Rayleigh wave low-Vs zones. Images made with the Mendocino data clearly show rapidly decreasing lithosphere-asthenosphere boundary depths from the subduction to transform regime.

Sarahsaurus aurifontanalis is the most recent sauropodomorph dinosaur to be discovered and named from the Early Jurassic of North America. The dinosaur is represented by a mostly complete and articulated holotype specimen that preserves a unique manual phalangeal count of 2-3-4-2-2 and accessory pubic foramen adjacent to the obturator foramen. The holotype of Sarahsaurus comprises a braincase and isolated cranial elements, but the skull previously referred to this taxon, MCZ 8893, can only be provisionally referred to Sarahsaurus until additional crania are found associated with postcranial material. Sarahsaurus comes from the middle third of the Kayenta Formation, which is considered to be Early Jurassic in age despite the absence of a radiometric date from that unit. A new technique used to obtain a U-Pb radiometric date from the type quarry of Sarahsaurus in the Kayenta Formation was influenced by secondary uranium enrichment in the open system of the fossil bone. That suggests that uranium within the Kayenta Formation may be the result of the movement of groundwater during the Laramide orogeny in the Late Cretaceous and Early Eocene, and lends support to the hypothesis that the uplift of the Colorado Plateau began relatively early in Late Cretaceous to the Eocene. / text

Isolating the climatic mechanisms driving Holocene geomorphic change and deciphering the role of landscape change in prehistoric cultural processes both require well-dated and relatively continuous alluvial chronologies. This study presents a centennial-scale, latest Pleistocene and Holocene chronology based on alluvial fan, floodplain, groundwater-discharge, and volcanic deposits for the Carrizo Wash watershed, a Little Colorado River headwater drainage on the southeastern Colorado Plateau. More than 200 radiocarbon dates provide chronometric control. The age of Zuni Salt Lake volcanic eruptions was re-evaluated using radiocarbon and luminescence dating. Two eruptive phases ~13.3 ka and ~11.8 ka suggest closely spaced, monogenetic events. These terminal Pleistocene ages for the eruptions are significantly younger and substantially more precise than previous argon method ages. Sediment exposed in modern arroyos is dominated by middle Holocene (~7.1–4.9 ka) alluvium in valley contexts, whereas piedmont alluvium dates primarily to the late Holocene (~4.3–2.7 ka). Extensive prehistoric channel entrenchment occurred ~4.9 and 0.8 ka. Localized incision occurred ~1.9 and 1.2 ka, and possibly ~7.5 and 2.7 ka. Extended drought typically preceded arroyo cutting, and entrenchment was associated with increased climate variability, major shifts in precipitation amount or seasonality, and reduced flooding. Accelerated valley and piedmont aggradation appears related to increased flooding and runoff associated with reduced vegetation cover during periods of low effective moisture resulting from enhanced North American Monsoon circulation and weak ENSO conditions. Conversely, slow or stalled deposition appears connected to reduced flooding and runoff fostered by denser vegetation during times of increased effective moisture caused by enhanced El Niños and increased winter precipitation. Ground-water discharge deposits at Cienega Amarilla indicate that spring discharge was greatest and water tables most elevated ~2.3–1.6 ka. Spring discharge appears to reflect variations in El Niño frequency and intensity and the resultant variations in winter precipitation. Study results suggest that predicted increased drought and enhanced or delayed monsoons associated with modern climate change could initiate accelerated erosion of upland areas and increased flooding in southern Colorado Plateau headwater tributaries. Archaeological implications include temporal biases associated with surface site distributions and changing viability of floodwater and water-table farming over time.

The historically introduced House Rock Valley bison herd has, in recent years, migrated from the eastern Arizona Strip onto the Kaibab Plateau within Grand Canyon National Park. Bison are considered a nonnative species to the southern Colorado Plateau, and the animals adversely impact sensitive ecosystems prompting National Park Service wildlife managers to pursue their removal. Archaeofaunal evidence of bison in the Grand Canyon and neighboring regions, however, raises concern that bison may in fact be native. Assessing the evidence within a zooarchaeological interpretive framework is critical since mere presence/absence lists of bison remains do not address the potentially complex cultural processes involved in the formation of archaeofaunal assemblages. Inter-assemblage comparisons illustrate a decline in relative abundance and skeletal completeness correlated to distance from traditionally understood historical bison distribution. If bison were present in the Southwest, as the evidence suggests, they likely entered the region only occasionally as small, dispersed herds.

The ~5.6-4.8 Ma Bouse Formation, exposed along the lower Colorado River, contains a well exposed but debated record of river integration. Sedimentologic and stratigraphic analysis aid interpretation of depositional processes, relative water depth, depositional environments, stratal architecture, and basin-filling history. Data collected include detailed measured sections, facies descriptions, and fault measurements. Seven lithologically distinct units have been identified along with numerous marine sedimentary structures and fossils. The Bouse Formation preserves a systematic sequence-stratigraphic architecture that records two cycles of base level rise and fall. Lacustrine versus estuarine interpretation remains elusive, though new isotope and micropaleontology data suggest a shift from marine to lacustrine. Constructed stratigraphic facies panels reveal a wedging geometry indicative of syn- to post-depostional tilting, leading us to propose a "sag basin" model during deposition of the Bouse. Finally, the newly described Bouse upper limestone unit resolves a long-standing debate over the age of the first through-going river.

abstract: For this dissertation, three separate papers explore the study areas of the western Grand Canyon, the Grand Staircase (as related to Grand Canyon) and Desolation Canyon on the Green River in Utah. In western Grand Canyon, I use comparative geomorphology between the Grand Canyon and the Grand Wash Cliffs (GWC). We propose the onset of erosion of the GWC is caused by slip on the Grand Wash Fault that formed between 18 and 12 million years ago. Hillslope angle and channel steepness are higher in Grand Canyon than along the Grand Wash Cliffs despite similar rock types, climate and base level fall magnitude. These experimental controls allow inference that the Grand Canyon is younger and eroding at a faster rate than the Grand Wash Cliffs. The Grand Staircase is the headwaters of some of the streams that flow into Grand Canyon. A space-for-time substitution of erosion rates, supported by landscape simulations, implies that the Grand Canyon is the result of an increase in base level fall rate, with the older, slower base level fall rate preserved in the Grand Staircase. Our data and analyses also support a younger, ~6-million-year estimate of the age of Grand Canyon that is likely related to the integration of the Colorado River from the Colorado Plateau to the Basin and Range. Complicated cliff-band erosion and its effect on cosmogenic erosion rates are also explored, guiding interpretation of isotopic data in landscapes with stratigraphic variation in quartz and rock strength. Several hypotheses for the erosion of Desolation Canyon are tested and refuted, leaving one plausible conclusion. I infer that the Uinta Basin north of Desolation Canyon is eroding slowly and that its form represents a slow, stable base level fall rate. Downstream of Desolation Canyon, the Colorado River is inferred to have established itself in the exhumed region of Canyonlands and to have incised to near modern depths prior to the integration of the Green River and the production of relief in Desolation Canyon. Analysis of incision and erosion rates in the region suggests integration is relatively recent. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

The Little Grand Wash fault and the Salt Wash Graben in the Colorado Plateau of southeastern Utah emit CO2 gas from abandoned drillholes, springs, and a hydrocarbon seep. Similar CO2-charged water has also been emitted in the past, as shown by large localized travertine deposits and veins along and near the fault traces. The faults cut natural CO2 reservoirs and provide an excellent analog for geologic CO2 sequestration. The faults cut a north-plunging anticline of rocks consisting of siltstones, shales, and sandstones from the Permian Cutler Formation through the Cretaceous Mancos Shale. The Little Grand Wash fault has 260 m of throw and the stratigraphic separation across the Salt Wash Graben is 50 m. The fault rocks in the damage zone show hundreds of fractures, which decrease in density farther away from the faults. In specific areas, fractures with the presence of calcite mineralization indicate fluid migration and bleach zones from a few millimeters to 30 cm. This is evidence of past fluid migration directly associated with the fault zone. Calcite mineralization fills these fractures and is also deposited in a variety of other bed forms. Foliated fault gouge, 5 to 20 cm thick, forms clay smear structures with a scaly shear fabric in a zone l0 to 15 cm thick is seen in the fault core. The leakage is constrained to the footwalls of the northernmost faults throughout the area. Clay-rich gouge structures should be effective barriers to cross-fault flow . Well log, surface geologic, and geochemical data indicate that the CO2 reservoirs have been cut by the faults at depth, providing a conduit for the vertical migration of CO2 to the surface, but not for horizontal flow across the fault plane. Even though lateral cross-fault migration may be impeded, this study clearly indicates that there are possible migration pathways for the escape of CO2 from faulted subsurface aquifers, including aquifers faulted by "low-permeability" faults with clay gouge. Three-dimensional flow models show how the fault's maximum permeability in the damage zone is parallel to the faults, and the leakage though the damage zone is localized near the fold axis of the regional anticline. Direct dating of the clay in the fault gouge was done by ExxonMobil with 40Ar/39Ar methods, indicating that fault movement occurred between the middle Eocene and the end of the Miocene. During this time, the Colorado Plateau is interpreted to have been experiencing rapid uplift. The middle Jurassic, upper Jurassic, and Cretaceous rocks at the surface have been uplifted approximately 1.8 km since the end of the Eocene. This uplift may have influenced fault movement in the Colorado Plateau and along the Little Grand Wash fault, and Salt Wash and Ten Mile Graben. In evaluating these deep aquifers for CO2 sequestration, careful design and monitoring of the geological structure and stress regimes must be considered to avoid leakage.

This dissertation encompasses two studies: one developing virtual field trips for mobile devices for an innovative approach to lower-division geoscience education, and the other examining the role of rock strength in river erosion and landscape evolution. The education study involves the development of three virtual field trip modules (Geologic Time, Geologic Structures, and Hydrologic Processes, all free on iTunes and Google Play) that lead students down a virtual Colorado River through Grand Canyon by physically moving around their campus quad, football field or other location, using their GPS-equipped smart phone or tablet. As students reach each location in the scaled down and geo-referenced virtual Grand Canyon, an informative video appears with a themed geological question and an interactive touchscreen activity. The effectiveness of these three modules in terms of student engagement and learning was tested at five U.S. Colleges with a range of missions and student demographics. Results show that the virtual field trip modules are effective at increasing student interest across races and genders in the geosciences, do not detract from student learning, and have the potential to increase content comprehension. The second study is the examination of the relation between rock strength and topography in the Colorado Plateau. This work contributes empirical data to the age-old debate over the mechanisms and patterns of stream erosion through statistical relations between rock strength and stream power, river steepness, and valley width along the Green-Colorado River system. Estimates of an “effective” tensile strength were calculated for units too incompetent to test directly, such as the shales prevalent in the region. Results indicate bedrock strength is a first-order control on river erosion in this landscape, as suggested by John Wesley Powell in 1896: “where the rocks are firm and stable, corrasion [sic] of the stream is slow; where the rocks are soft, corrasion [sic] is more rapid,” which is intuitive yet frequently overlooked.

In the past decade there has been a call for integrated studies that examine the interaction of fluvial and aeolian processes (Belnap et al., 2011; Bullard and Livingstone, 2002). In this study, we examined the role of land-use, weather, and soil type on the flux of aeolian material into dry washes on the Colorado Plateau in central Utah, USA, and western Colorado, USA. Our goal was to quantify the impact of individual deposition and erosion events by correlating weather and land-use data with a combination of measurement methods including dust collection via dust traps, GPS surveying, and close-range photogrammetry. Our data suggest that there is an interaction between these processes and that seasonality and land-use play a large role in determining the strength of this interaction. Particularly, high land-use and dry, windy conditions were most conducive to the surface movement of sediment and subsequent removal of that sediment by fluvial processes.

What were Mary-Russell Ferrell Colton’s contributions to the progressive education movement and the Indian arts and crafts movement in the Southwestern United States at a time when the region was still very remote? Artist, author, amateur ethnographer, educator, and curator; these were but a few of the talents of Mary-Russell Ferrell Colton, co-founder of the Museum of Northern Arizona and early art advocate on the Colorado Plateau. This study investigates how Colton contributed to the progressive education movement and the Indian arts and crafts movement through the work that she did at the museum. There, she labored to increase public awareness of the importance of art education and to revive Native American arts on the Colorado Plateau. Using an extensive collection of archival material in the Colton Collection at the Museum of Northern Arizona, as well as oral history interviews, this historical study provides a nuanced analysis of Colton’s life as an educator. Colton’s influence is not well known today, but her professional contributions merit recognition, giving her a place in the history of American education. This study reveals how Colton’s efforts fit within the context of the work of her contemporaries in Santa Fe and Taos, and within the progressive education movement, from the then relatively remote outpost of Flagstaff. Much can be learned from Colton’s work that is relevant to the field of education today. Her ideals and writings about art education will resonate with opponents of No Child Left Behind. Colton’s work as one of northern Arizona’s earliest art educators contributed to a better understanding of the culture of the various peoples of the Colorado Plateau and to the preservation of Navajo and Hopi traditions through education. Colton made notable contributions to the Indian arts and crafts movement, museum education, and the progressive education movement. A woman of firm convictions and ideals, Colton was strong-willed, and complex, a multi-faceted person with a broad range of interests which she pursued with passion and commitment. This study crosses the boundaries of several disciplines, including educational history, museum studies, women’s studies, educational biography, Native American studies, and art education.