This study identifies the biogeographic factors that structure small mammal communities on mountains of the Colorado Plateau and adjacent regions. Forty six isolated ranges were characterized across a 5-state study area encompassing the Colorado Plateau, including the central high plateaus of Utah and the Basin and Range Province (i.e. the Great Basin and mountains of Arizona and New Mexico). Presence/absence data of 25 montane mammal species were used to explore the interactions between historical and ecological processes affecting local and regional diversity patterns. Multivariate analyses, such as non-metric dimensional scaling, were used to explore factors which influence community composition. Results of these analyses revealed the Colorado River as a significant biogeographic barrier that affects montane mammal community structure. MtDNA cytochrome b sequence variation was analyzed among populations of the long-tailed vole, Microtus longicaudus, sampled from five interior ranges of the Colorado Plateau- Abajo, LaSal, Henry, and Chuska Mts., and Boulder Mountain of the Aquarius Plateau-and analyzed using traditional phylogenetic approaches (parsimony and likelihood) as well as nested clade analysis. Results support previous documentation of a major east-west phylogeographic break occurring between populations southeast of the Colorado River (eastern Arizona, Colorado, Wyoming and New Mexico) and all other western populations, which include a central clade, a northwest clade, and an Alaskan island clade. Evidence also supports differentiation of a 'southern Rockies' clade and a distinct 'southwest island' clade. Populations of M. longicaudus north and west of the Colorado River (Boulder and Henry Mts.) share two haplotypes, form a well-supported subclade with populations from the Kaibab plateau, and are closely related to the Northwest clade. Past approaches to studying montane mammal communities utilizing theory based on island biogeography have overemphasized area and isolation as the only forces structuring insular communities. As a result, there has been a lack of recognition of the influences of environmental factors, species turnover, and barriers that create and maintain regional diversity on the Colorado Plateau and adjacent areas.

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This thesis was written to outline the history of five stone houses, which have survived almost a century of mining activity. The houses are located on a barren mesa, called Calamity, in southwestern Colorado. This work was funded by the Bureau of Land Management, Department of the Interior, in order to explore the possibility of designating this site as a National Historic Site. Men and women lived and worked on this and the surrounding mesas for most of the twentieth century. The lives of the families, the men, women, and children who lived and worked on Calamity Mesa, provided the context for the entire period. These people formed nebulous communities on what could only be called a twentieth-century frontier. I used several methods for this study, including oral interviews with surviving miners and their families, company and government officials, mining engineers, and medical personnel involved in studies concerning the effects of radiation exposure. Government publications, local newspapers, and personal papers of several individuals were also researched. Through the use of these methods I further developed the history of the period, by focusing on Calamity Camp and the lives of the men and women who lived and worked there. The miners who came to Calamity Mesa extracted the carnotite ore from sandstone beds. Originally, miners searched for radium, desired for its illusory cure for cancer. Then they sought vanadium, which was used as a strengthening agent for steel during both world wars . Finally, their goal was uranium, a key component for the production of nuclear weapons and energy. The search for these minerals brought, many working class men and women to the Colorado Plateau. They brought their families to Calamity Mesa and lived in whatever shelter they could find. The stone houses, lived in by generation after generation of miners and their families, who came searching for carnotite, provided a permanence to Calamity Mesa throughout this period.

Robust interpretations of rock thermal histories are critical for resolving the timing and rates of geologic processes, especially as low-temperature thermochronology has become a common tool for investigating the evolution of landscapes and mountain belts and the feedbacks between geodynamic processes. Most interpretations of thermochronologic cooling ages, however, attribute rock cooling entirely to rock exhumation - a common but tenuous assumption in many settings where thermochronology is used to investigate links between tectonics, climate, and landscape evolution, because these places often have history of magmatism. Exploring the complexities - and advantages - of interpreting low-temperature thermochronologic data in magmatic terranes is the principal theme of this work. Using simple analytical approximations as well as the finite-element code Pecube, we characterize the cooling age patterns inside and around plutons emplaced at upper and middle crustal levels and identify the advective and conductive scaling relationships that govern these patterns. We find that the resetting aureole width, the difference between reset and unreset cooling ages in country rocks, and the lag time between pluton crystallization age and pluton cooling age all scale with exhumation rate because this rate sets the advective timescale of cooling. Cooling age-elevation relationships in these steadily exhuming models have changes in slope that would masquerade as changes in exhumation or erosion rates in real datasets, if the thermal effects of the plutons were not accounted for. This is the case both in the country rocks immediately next to upper crustal plutons and, surprisingly, in the country rocks kilometers above mid-crustal plutons with no surface expression. Together with a lag-time analysis useful for the practical question of when it is appropriate to interpret a cooling age as an exhumation rate in crystalline rocks, this work improves our framework for evaluating the effects of magmatism on thermochronologic datasets. We also demonstrate the importance of considering the magmatic history of a region in field studies of the Colorado Plateau, where interpreting apatite (U-Th)/He data requires diagnosing significant inter- and intra-sample age variability. Prior to considering the thermal history of the region, we develop a new model for a common source of this age variability: excess He implantation from U and Th (i.e., eU) hosted in secondary grain boundary phases (GBPs), which can make very low eU apatites hundreds of percent 'too old'. Samples significantly affected by He implantation are not useful for thermal history interpretations, but this model does provide a diagnostic tool for discriminating these samples from those with useful age trends. Once the effects of GBPs have been accounted for, the remaining data from two different thermochronologic archives in the central Colorado Plateau provide a new perspective on the Cenozoic history of the region, which has a multiphase - and enigmatic - history of magmatism and erosion. We find that sandstones in the thermal aureoles around the Henry, La Sal, and Abajo mountains intrusive complexes were usefully primed by magmatic heating in the Oligocene to document the subsequent late Cenozoic history of the region more clearly than any other thermochronologic archive on the Plateau. These data document a stable Miocene landscape (erosion rates<30 m/Ma) that rapidly exhumed ~1.5-2 km in the Plio-Pleistocene (~250-700 m/Ma no earlier than 5 Ma) in the Henry and Abajo mountains, and strongly suggest most of this erosion occurred in the last 3-2 Ma. The integration of the Colorado River ca. 6 Ma, which dropped regional base-level, is the principal driver of this erosion. It is likely, however, that a component of the rapid Pleistocene rock cooling is unique to the high mountains of the Colorado Plateau and reflects an increase in spring snow-melt discharge during glacial periods. Although apatite thermochronology results far from the Oligocene intrusive complexes cannot resolve this detailed Plio-Pleistocene history, they do constrain the onset of late Cenozoic erosion to no earlier than ~6 Ma. Moreover, apatite cooling ages from these rocks also document Oligocene cooling (ca. 25 Ma) that is contemporaneous with the emplacement of the laccoliths and the waning of the vigorous magmatic flare-up that swept through the southwestern USA ca. 40-25 Ma. Although the cooling ages are consistent with ~1 km of exhumation in the late Oligocene and early Miocene, as previous workers have suggested in the eastern Grand Canyon region, we demonstrate that a transient change in the geothermal gradient (peaking at ~50˚C/Ma in the late Oligocene) driven by moderate mid-crustal magmatism can produce identical age patterns. Therefore, we re-interpret the mid-Cenozoic erosion event on the Colorado Plateau as primarily a change in the crustal thermal field, rather than an erosional event. This requires a more significant Laramide-age unroofing in parts of the central Plateau and perhaps a re-evaluation of the interpretations of Oligocene canyon cutting in the Grand Canyon region

The debris-flow initiation variable of clay mineralogy is examined for Holocene age debris-flow deposits across the Colorado Plateau. A Kolmogorov-Smirnov two-sample test between 25 debris-flow producing shale units and 23 shale units rated as not producing debris-flows found a highly significant difference between shale unit kaolinite-illite and montmorillonite clay content. Debris-flow producers tend to have abundant kaolinite and illite (61.5% of clays) and small amounts of montmorillonite (10.4%). Clay sample soluble cation (Na, Ca, K, and Mg) content could not be used to accurately divide the data set into debris-flow producers and debris-flow non-producers by either cluster analysis or a Kolmogorov-Smirnov two-sample test.AVIRIS hyperspectral data reveal that debris-flow deposits, colluvium, and some shale units in Cataract Canyon, Utah display the double-absorption feature characteristic of kaolinite at 2.2 µm. Lab-based reflection spectra and semi-quantitative x-ray diffraction results show that Cataract Canyon debris-flow matrix clays are dominated by kaolinite and illite and lacking in montmorillonite. A surface material map showing the spectral stratigraphy of the study area was created from AVIRIS data classified using an artificial neural network and compares favorably to existing geologic data for Cataract Canyon. A debris-flow initiation potential map created from a GIS-based analysis of surface materials, slope steepness, slope aspect, and fault maps shows the greatest debris-flow initiation potential in the study area to coincide with outcrops of the Moenkopi Formation on steep (&gt;20%), southwest-facing slopes. Small areas of extreme debris-flow initiation potential are located where kaolinite and illite clay-rich colluvial wedges are located on southwest-facing walls of Colorado River tributary canyons. The surface materials map shows formations clearly when they remain relatively consistent in composition and exposure throughout the study area, such as the White Rim Sandstone and most clay-rich members of the Moenkopi Formation. The debris-flow producing Organ Rock Shale and Halgaito Formation were shown inconsistently on the surface materials map, likely as a result of compositional variations in the study area. The results of this study provides evidence that hyperspectral imagery classified using an ANN can be successfully used to map the spectral stratigraphy of a sparsely vegetated area such as Cataract Canyon.

This dissertation investigates the crustal structure of the eastern Basin and Range Province in the western United States and its relationship with the present-day extensional regime governing this region. The use of combined results from different geophysical methods provide a better understanding of the subsurface crustal structure and the processes involved in this extensional deformation. Teleseismic receiver functions were used to create a uniformly sampled map of the crustal thickness variations and stacked images of the crust beneath the majority of the state of Utah, which provide additional constraints on the seismic characteristics of the crust and upper mantle. These results reveal crustal variations characterized by a distinct change in crustal thickness that closely follows the surface trace of the Wasatch fault, with differences in depth of up to 10 km across a distance of less than 55 km. Analysis of seismic reflection profiles, horizontal and vertical crustal velocities from continuous GPS, and surface geology provide new constraints on the relationships between interseismic strain accumulation, subsurface fault geometry, and geologic slip rates on seismogenic faults. Seismic reflection data show recent activity along high-angle normal faults that become listric with depth, sole into preexisting décollements, reactivating them, and appear to be connected at depth with a regionally extensive detachment horizon. GPS data reveal present-day crustal extension of ~3 mm/yr and no net vertical motion between the Colorado Plateau and eastern Basin and Range. Inverse modeling results of the crustal deformation data include a low-angle dislocation (~8-20°) at a locking depth of ~7-10 km, consistent with the interpreted seismic data, and slipping at 3.2±0.2 mm/yr, suggesting an active regionally extensive sub-horizontal surface beneath the eastern Basin and Range. A test of this hypothesis using seismic data interpretation as the basis for a forward strain accumulation model shows that displacement across a deep low-angle detachment imaged seismically is also consistent with geodetic velocities. Seismic and geodetic data support a model for eastern Basin and Range mechanics wherein diffuse permanent strain of the upper crust by multiple discrete faults is facilitated by displacement along a single low-angle detachment at midcrustal depth.

Most approaches to interpreting alluvial records in drylands fall into one of two categories: (1) The "arroyo problem," wherein workers study cycles of streambed aggradation and degradation in broad, unconstricted alluvial valleys; and (2) paleoflood hydrology, where alluvial sequences in constricted bedrock canyons are interpreted as paleoflood deposits from streams with stable channel grade and geometry. Both approaches can be valid in their end-member settings, but there is confusion about how the two record types relate in a single drainage. We address this disconnect in Buckskin Wash, an ephemeral stream that consists of a broad alluvial reach draining into a tightly constricted slot canyon. By employing detailed sedimentology, stratigraphy, and geochronology in both the alluvial and constricted reaches of the watershed, we test the hypothesis that the slot canyon deposits are anticorrelated to valley-fill deposits upstream, implying that arroyo cutting is driven by episodic flooding. Alluvial reach deposits are characterized by stratal packages representing incremental, long-term aggradation bound by erosion surfaces representing channel entrenchment. At least four packages younger than ~3 ka are present, the youngest spanning ~0.7 - 0.15 ka. Each is composed of interfingering imbricated gravels, laminated sands, and massive silty clays. Constricted reach deposits consist of five discrete packages, each composed of tabular beds of laminated silty sand that were deposited relatively rapidly. The oldest package dates to ~1.9 - 1.1 ka, whereas the rest of the deposits are younger than ~0.15 ka. Traditional paleoflood techniques would suggest that the constricted reach deposits record a ~1000-year absence of paleofloods followed by ~100 years of frequent, high-magnitude flooding that indeed correlate to arroyo cutting upstream. We argue instead that the constricted reach deposits record an episode of higher preservation potential. Transport of sediment from the alluvial reaches during historic arroyo cutting likely led to a pulse of sediment storage and changed stage-discharge relations in the slot canyon downstream, allowing even moderate floods to overtop existing deposits and be preserved. This new interpretation suggests that, because preservation may be a function of episodic sediment loading from upstream, constricted-reach deposits may not accurately record the paleoflood history of a stream.

Fossil plants in the Upper Triassic Chinle Formation are preserved in fluvial channel, overbank, and lacustrine deposits. Plant-bearing units in these deposits are classified into seven types based on these depositional environments or subenvironments. Taphonomic characteristics of these assemblages, and of individual plant fossils within them, indicate that most plant fossils have either not been transported far from their growth sites or are preserved in situ. One particular deposit in the central part of Petrified Forest National Park preserves fossil plants in three associations: (1) allochthonous logs in basal lags in a channel-fill/lateral accretion deposits; (2) autochthonous horsetail trunks and parautochthonous horsetail leaves in a crevasse-splay deposits; and (3) parautochthonous and autochthonous cycadaceous, fern and other types of leaves, and erect and prostrate trunks in a paludal/distal splay deposits. Exposures of contemporaneous high-sinuosity channel and overbank deposits in this area enabled the reconstruction of the local paleogeography, paleohydrology, and paleoecology at a high resolution. Fossil plant assemblages of the Upper Triassic Chinle Formation are concentrated in the lower members of the formation. The lower part of the Chinle Formation was deposited in an incised valley system. Depositional, hydrological, and near-surface geochemical conditions in the incised valley system were conducive to preservation of terrestrial organic material, even though regional conditions were characterized by seasonal/monsoonal precipitation and groundwater conditions. Fossil plant assemblages preserved in these types of fully terrestrial incised valley-fills are taphonomically biased towards riparian wetland environments.

Fluvial terraces contain information about incision, deformation, and climate change. In this study, a chronostratigraphic record of Colorado River terraces is constructed from optically stimulated luminescence (OSL) dating of Pleistocene alluvium and real-time kinematic (RTK) GPS surveys of terrace form. This record is analyzed to relate terrace formation to late Pleistocene climate fluctuations, and terrain analyses and longitudinal profile patterns reveal recent salt-related activity in the northern Paradox Basin as well as patterns in Colorado Plateau incision. A well-preserved, correlative suite of mainstem (M) fluvial deposits exists along the Colorado River upstream of Moab, Utah. Absolute dates indicate sedimentation >70 ka (M7, M6/M5), 70-50 ka (M4), 50-40 ka (M3), and 35-25 ka (M2). The M4 and M2 formed during the crescendo to glacial maxima, but the M7, M6/M5, and M3 were deposited during variable climate of marine isotope stages (MIS) 5 and 3. Deposits include thin (<7 m) strath terraces and thick (10-20 m) fill terraces. Our results suggest that terrace sedimentation is linked to enhanced sediment flux during glaciations in Rocky Mountain headwaters (M4 and M2), but major deposits also formed during dryland tributary sediment loading with markedly different timing (M6/M5 and M3). Conversely, incision may be driven by higher deglacial flows. Clast provenance data demonstrate greater percentages of locally-sourced sediment in M6/M5 and M3 deposits. Valley-bottom geometry and neotectonics control terrace form, with strath terraces found in bedrock-restricted reaches and fill terraces in wider valleys. Previously speculated salt deformation in this area is confirmed by localized collapse preserved in M4 stratigraphy in the Cache Valley graben and ~15 m of broader subsidence upstream. Concavity and knickzone distributions in tributary profiles are discordant and represent subtle expressions of salt-tectonic activity. Finally, a surprisingly rapid incision rate of ~900 m/Ma over the past ~70 ka suggests that the Colorado River may be responding to flexural rebound in the central plateau, but is faster than that predicted by the debated bull's-eye pattern of regional incision. This locally high rate may also reflect a transient wave of incision, as suggested by increased Pleistocene rates interpreted by studies in Glen and Grand canyons.

Extensive research exists regarding invasive alien plant species including impacts to native ecosystems and efficacy of control methods on public lands and river corridors. Many studies have identified the need for more research regarding the social implications of invasive alien species management. More specifically, additional research is needed regarding the impacts of invasive alien plant management on the Colorado Plateau to river-based recreation experiences. It is important for public land management agencies like the National Park Service to understand recreation-based stakeholders’ knowledge, norms, and preferences toward managing prevalent alien plants like tamarisk. For this study, 330 river users were questioned about their knowledge of tamarisk and preferences for tamarisk management on the Green and Colorado River corridors of the Colorado Plateau. Results show that a majority of river users want tamarisk to be removed. The tamarisk control methods investigated in this thesis were also evaluated by respondents as acceptable. The methods evaluated to be the most acceptable were the cut-stump method and the use of tamarisk leaf beetle, while prescribed fire and the use of a machine to mulch tamarisk were found to be less acceptable. The use of chainsaws to perform the cut-stump method was found to be acceptable in both the Green and Colorado River corridors. This thesis concludes with a summary of findings and implications for land managers and future research.