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xxviii, 463 p. : ill., maps. A print copy of this title is available through the UO Libraries under the call number: KNIGHT F868.M65 J45 1991 / The environmental context and chronology of the transition from Early Holocene Lake Mojave to Middle Holocene Pinto cultural complexes of the southern California deserts has long been debated. This dissertation re-examines that debate, based on excavations at two major sites, and a rethinking of our most basic assumptions concerning culture change, cultural ecology, site formation processes, and dating techniques. Archaeological data recovered from two Lake Mojave/Pinto sites at Fort Irwin, in the Central Mojave Desert, were analyzed in order to track chronologically sensitive shifts in Lake Mojave-Pinto artifact assemblages through time. The archaeological assemblages recovered from Rogers Ridge and the Henwood sites were carefully analyzed into 36 depositional/analytical components for this task. Defining and chronologically ordering these assemblages required systematic consideration of artifact distributions and the development and application of 3 obsidian hydration rates based on associations with twelve 14C dates. The analysis shows that the Pinto Complex occurred in three phases. Phase I, ca. 8,200 to 7,500 BP, is marked by the addition of Pinto points to the Lake Mojave assemblage and a continuation of the basic Lake Mojave settlementsubsistence patterns. Phase II, 7,500 to 5,000 BP, is marked by the gradual disappearance of Lake Mojave points from the archaeological assemblages. Dramatic decreases in assemblage size and increases in assemblage diversity mark changing logistical strategies to infrequent and specialized site use. Phase III, 5,000 to 4,000 BP, is marked by a strong predominance of Pinto points and slightly larger assemblages. Patterns of variation among assemblages suggest that logistical strategies continued to emphasize infrequent and specialized site useage. The link between environmental change and shifting settlement-subsistence strategies was apparently relatively direct during the Pinto period, Environmental changes during the Early Holocene (11,000 to 8,000 BP) Mojave Desert led to subsistence stress among populations of the Pinto Complex. Cultural adjustments resulted in smaller human populations moving through larger home territories. It is suggested that critical thresholds in communication and mating networks were crossed which resulted in the collapse of social systems in the Mojave Desert about 7,000 BP. / Committee in charge: C. Melvin Aikens, Ann Simonds, Don E. Dumond, and William Loy

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UA Open Access Publishing Fund / We examined a secondary contact zone between two species of desert tortoise, Gopherus agassizii and G. morafkai. The taxa were isolated from a common ancestor during the formation of the Colorado River (4–8 mya) and are a classic example of allopatric speciation. However, an anomalous population of G. agassizii comes into secondary contact with G. morafkai east of the Colorado River in the Black Mountains of Arizona and provides an opportunity to examine reinforcement of species’ boundaries under natural conditions. We sampled 234 tortoises representing G. agassizii in California (n = 103), G. morafkai in Arizona (n = 78), and 53 individuals of undetermined assignment in the contact zone including and surrounding the Black Mountains. We genotyped individuals for 25 STR loci and determined maternal lineage using mtDNA sequence data. We performed multilocus genetic clustering analyses and used multiple statistical methods to detect levels of hybridization. We tested hypotheses about habitat use between G. agassizii and G. morafkai in the region where they co-occur using habitat suitability models. Gopherus agassizii and G. morafkai maintain independent taxonomic identities likely due to ecological niche partitioning, and the maintenance of the hybrid zone is best described by a geographical selection gradient model.

The efficacy of providing water sources in desert ecosystems to enhance wildlife populations and their distribution continues to be debated among wildlife managers. Some argue wildlife water developments provide a direct benefit to numerous species, while others point to the potential that wildlife water developments alter competition or predation dynamics and disrupt native communities. Additionally, some have argued that the availability of water may become more important to wildlife in the face of vegetative changes associated with expansive fire and conversion of shrub or forest lands to grasslands which alters the thermal landscape available to animals. I evaluated the influence of free water and expansive fire on aspects of the ecology (habitat selection, space use and survival) of Gambel's quail (Callipepla gambelii) in the Mojave Desert of southwestern Washington County, Utah, USA. I attached radio-transmitters to a total of 206 quail (74 adult males, 67 adult females, and 65 juvenile males and females) and monitored them from 2010 – 2013. For chapter one of my thesis, I evaluated the response of marked quail to removal of access to water in a before-after controlled impact (BACI) design. I found little influence of water removal on survival as models with this effect received little to no support and overlap in confidence intervals occurred between treatment and reference groups. Likewise, the distance from the center of the summer home range to the nearest water source did not differ by year (F = 1.63; P = 0.19) or treatment (removal of water) (F = 0.89; P = 0.35) and pairwise comparisons of distances for the treatment by year interaction were not significant (P > 0.05 in all cases). For size of home range area, however, I found strong effects for year (F = 3.07; P = 0.03), treatment (F = 4.67; P = 0.03), and their interaction (F = 7.61; P = 0.01). Mean home range size for quail was 6.10 and 1.63 km2 for animals in the reference area during treatment years (2012 and 2013) compared to 5.07 and 8.99 km2 for quail in the treatment area during 2012 and 2013, respectively. Removal of water influenced size of summer home ranges, but not the location of the summer home range or survival rates. I hypothesize that removal of access to free water required quail in the treatment area to expand their space use patterns in 2013 in order to satisfy water demands via pre-formed water. For chapter two of my thesis, I evaluated habitat selection of Gambel's quail in relation to vegetation type, topographic features, water, and recent (4-7 years) expansive fire. Gambel's quail selected areas of decreased roughness which were closer to water and fire boundaries than random locations. I found that quail preferred moderate (< 10 degrees) hillsides and ravine bottoms. I found no evidence that quail avoided the burned areas within their home ranges and 80% of their telemetry points were <500 meters from a burn edge. The Beaver Dam slope topography strongly influenced habitat selection for Gambel's quail and they showed strong selection for water sources during summer months. These data also suggest that wildfires have had limited impact on habitat selection by this species, four to seven years later.

One of the important contributions genetic studies have made to conservation is the ability to resolve taxonomy and define relationships among populations. However, this can be complicated when species exhibit hybridization. Hybridization can be an important part of the evolutionary process and a critical component in a species ability to adapt to a changing environment. Most hybrid zones are observed at ecotones between two distinct habitats and this may be important in defining the role of hybrid zones in the evolutionary process. I examined hybridization among the three distinct lineages of desert tortoises in the genus Gopherus. An important aspect of this study system is the presence of areas of overlap between divergent lineages of desert tortoise which allowed me to test hypotheses about which forces influence these taxonomic boundaries. Specifically, I tested hypotheses about the contribution of physical vs. ecological segregation and the relative importance of isolation and gene flow in the formation of these disparate desert tortoise lineages. I used mtDNA sequence data and 25 microsatellite loci to perform Bayesian clustering, clinal analyses and habitat suitability modeling to infer population structure and influence of landscape features at each contact zone. In both instances, I observed ecological niche partitioning and limited hybridization at ecotones. I then used mtDNA and four nDNA loci to perform a multi-locus phylogenetic analysis to estimate the species tree among desert tortoise lineages and tested for ancestral admixture with RNA-seq data using demographic inference employed in the software package ∂a∂i. My results validate taxonomic distinction among all three lineages without evidence of ancestral introgression. These data suggest that despite the presence of contemporary hybridization and incomplete reproductive isolation, divergence among these lineages is consistent with species-level differentiation. By clarifying the evolutionary processes that influence the distribution of desert tortoise lineages, this study will directly inform efforts to preserve the evolutionary potential of these threatened species. Ultimately, understanding the evolutionary history of desert tortoises not only clarifies the forces that have driven speciation in this group, but it also contributes to our knowledge of the biogeographic history of the southwestern deserts and how diversity is maintained within them.

The sidewinder rattlesnake is found only in the low hot deserts of the southwestern United States and northwestern Mexico. It has adapted to this environment in various ways and thus is able to live under extremely demanding conditions. Previously published information on sidewinders is quite complete in certain respects and totally lacking in others. The present study represents an attempt to integrate the various aspects of sidewinder biology into a more cohesive unit. A large sidewinder population at Kelso Dunes, Mojave Desert, California, was intensively studied for three years. A number of parameters - physical, clmatic, behavioral and population - were investigated. Activity cycles are most closely tied to thermal regimes and considerably less so to rainfall and wind. An abundance of small mammal burrows on most of the study area provide thermal refugia on hot days and hibernacula during the winter. Because of the insulating properties of sand and the general lack of frost at Kelso, sidewinder hibernacula are probably scattered over the entire study area and appear to be rather superficial. Mating occurs generally in the spring and the young are born alive in early autumn. Whether the sidewinder reproductive cycle is annual or biennial was not determined. During warm weather sidewinders become active at dusk and may wander over the sand in any direction for over 1200 meters - mostly by sidewinding. The average distance travelled is much shorter, however. This nocturnal wandering probably serves as a dispersal mechanism, since mark and release studies showed no tendency towards homing or territorality. By midnight, however, even the most active sidewinders have formed resting craters and remain coiled therein until sunrise or later. Among rattlesnakes cratering is a feature unique to sidewinders. During the day the crater serves primarily for thermoregulation and less so for concealment, whereas at night this order of importance is reversed. Sidewinders prey upon any small reptile or mammal they can overpower and may actually do a considerable amount of feeding from ambush during the day. After feeding they become sedentary until digestion is largely completed, shifting position only to warm the food bolus during the day. Bio-telemetry studies indicated that the rate of heating or cooling may be more important in thermoregulatory behavior than the simple attainment of absolute thermal thresholds. On cool evenings sidewinders often bask on asphalt roads or railroad rails, using these surfaces as sources of reradiated heat. The sidewinder population is not uniformly distributed on the Kelso study area. More trackways were recorded in dune areas dotted with large clumps of vegetation with stable sand hummocks beneath them. In rockier areas with low vegetation and little sand, sidewinder trackways were few and mostly those of juveniles. This was attributed to inadequate burrows and the general lack of shade in such areas.

This research contributes to the field of land use planning by examining the effects of demographic trends--also known as demographic futures--on growth and development projections for seven communities in the Mojave Desert region of San Bernardino County, California. Demographic trends based on California Department of Finance projections and land development data supplied by the Southern California Association of Governments were obtained for each of the communities for the period between 1990 and 2001. By using a spatially explicit urban growth model, these trends and data were then used to allocate community-specific future growth for Adelanto, Apple Valley, Barstow, Hesperia, Twentynine Palms, Victorville, and Yucca Valley. The research compared three projected settlement densities for each community. These three densities were based on settlement trends between 1990 and 2001, on existing densities as of 2001, and on densities that had been derived from prior research in the Mojave Desert region as a whole. The overall effect of using demographic trends to estimate settlement densities results in less development of open space and undeveloped lands than under existing densities or densities derived from prior research. Indeed, using demographic trend-derived densities in place of existing densities resulted in nearly 3,900 more acres of vacant land in the seven communities remaining undeveloped by the year 2020. Similarly, using demographic trend-derived densities in place of densities developed by prior research resulted in nearly 22,000 more acres of vacant land in the seven communities remaining undeveloped by the year 2020. Differences in projected land use patterns based on demographic trends are a key point for land use planners to consider when determining future development in each of the communities. Accounting for these demographic trends provides a way of "fine tuning" projections to ensure that they are more representative of the needs and expectations of future populations.

Disseminated precious-metal mineralization occurs at the Morning Star deposit, in the upper-plate of the Morning Star thrust which represents intermediate age (105 and 90 Ma) faulting along the Mesozoic foreland fold and thrust belt (MFFTB). Deformation along the Morning Star thrust consists of both ductile and brittle events, and is different than deformation on other structures in the MFFTB in the northeastern Mojave Desert. The different style and episodic nature of deformation, together with the spatial relationship to the Teutonia batholith, accounts for mineralization on the Morning Star thrust and the absence of mineralization on other thrusts in the belt. Two stages of mineralization have been identified in the Morning Star deposit. Six distinct types of electrum have been identified. Electrum occurs as free grains, fracture fillings, or as inclusions in minerals during primary mineralization, and as rims around early electrum or as intergrowths with covellite and acanthite during secondary mineralization. Textures and compositions of the electrum and Ag+Au-sulfides indicate Au and Ag remobilization was isochemical in the lower portions of the deposit, while remobilization at upper levels of the deposit resulted in gold enrichment. Hydrothermal fluids (H₂O-CO₂-6 wt.% NaCl), that were driven by Late Cretaceous igneous activity, scavenged metals from the host rocks to form the Morning Star mineralization. Early mineralization is syn-tectonic, but the bulk of the mineralization is post-tectonics. The bulk of the main stage mineralization was precipitated into open spaces at temperatures between 280° and 330°C by a combination of reduction and increased acidity of the fluid due to wall rock reactions. Ore grades have subsequently been increased by Au and Ag remobilization. / Ph. D.

The purpose of this study is to investigate the level and distribution of genetic variation in Astragalus jaegerianus by using molecular markers. The objectives of the study are: to estimate levels of genetic variation within and among populations of Astragalus jaegerianus; to test the hypothesis that levels and patterns of genetic variation in species of restricted ranges and few individuals is low and partitioned at the population level; and to discern whether, or how well, genetic partitioning of Lane Mountain milk vetch correlates with its geographic partitioning in the field.