Geology Commons^™

Quantification Of Surface Roughness Of Lava Flows On Mars, Carolina Rodriguez Sanchez-Vahamonde

Electronic Thesis and Dissertation Repository

Volcanism has played a significant role throughout Mars’ geologic history. Extensive lava flows are widely spread across Mars’ equatorial region, shaping the surface in a very distinct way. In radar images (at the decimeter scale), these flows are bright, which is a typical characteristic of extremely rough, blocky lavas flows seen on Earth. Although the source of the extreme roughness of Martian lava flows is unknown, their surface roughness parameters can be constrained to 1) gain information about Mars’ interior processes, 2) find appropriate analogues on other planetary bodies, and 3) ideally infer the emplacement style of such lavas. Here, …

Evidence Of Limited Recruitment Of Pallid Sturgeon In The Lower Missouri River, Kirk D. Steffensen, Kimberly Chojnacki, Jeffrey A. Kalie, Meredith L. Bartron, Edward J. Heist, Kyle R. Winders, Nathan C. Loecker, Wyatt J. Doyle, Timothy L. Welker

United States Geological Survey: Staff Publications

Pallid Sturgeon Scaphirhynchus albus are endemic to the Missouri and Mississippi river basins and are rare throughout their range. The species was listed as federally endangered with little to no evidence of natural recruitment. Since population augmentation was initiated as a recovery objective in the early 1990s, thousands of hatchery-origin Pallid Sturgeon have been stocked in the lower Missouri River (Gavins Point Dam [river kilometer 1,305.1] to the confluence of the Mississippi River [river kilometer 0.0]). Efforts to discriminate natural reproduction and recruitment of wild-origin Pallid Sturgeon from hatchery-origin fish has been hampered by tag loss in hatchery-origin sturgeon, inconsistent …

Evidence Of Variable Climate And Resources During The Late Pleistocene And Holocene At Gona, Ethiopia, Marie White

Steeplechase: An ORCA Student Journal

The African Humid Period (AHP) spanned a period of approximately 15 to 5 thousand years ago (ka) and resulted in Northern and Eastern Africa being wetter than today. This climate change event impacted flora, fauna, and humans to an unknown extent. Much of the work on the AHP across Eastern Africa utilizes lacustrine and marine proxies rather than river-based (fluvial). Gona, located in the Afar region of Ethiopia, is known for its extensive archaeological and fossil records in fluvial deposits. However, the paleoenvironment of the AHP at Gona has not been investigated. This study uses stratigraphy, geochronology, and paleopedology to …

Seismic Evidence For Significant Melt Beneath The Long Valley Caldera, California, Usa, Ashton F. Flinders, David R. Shelly, Philip B. Dawson, David P. Hill, Barbara Tripoli, Yang Shen

United States Geological Survey: Staff Publications

A little more than 760 ka ago, a supervolcano on the eastern edge of California (United States) underwent one of North America’s largest Quaternary explosive eruptions. Over this ~6-day-long eruption, pyroclastic flows blanketed the surrounding ~50 km with more than 1400 km3 of the now-iconic Bishop Tuff, with ashfall reaching as far east as Nebraska. Collapse of the volcano’s magma reservoir created the restless Long Valley Caldera. Although no rhyolitic eruptions have occurred in 100 k.y., beginning in 1978, ongoing uplift suggests new magma may have intruded into the reservoir. Alternatively, the reservoir could be approaching final crystallization, with present-day …

Little Islands Recording Global Events: Late Quaternary Sea Level History And Paleozoogeography Of Santa Barbara And Anacapa Islands, Channel Islands National Park, California, Daniel R. Muhs, Lindsey T. Groves

United States Geological Survey: Staff Publications

Marine terraces are common on the Pacific Coast of North America and record interglacial high-sea stands superimposed on either stable or tectonically rising crustal blocks. Despite many years of study of these landforms in southern California, little work on terraces has been conducted on the two smallest of the California Channel Islands, Santa Barbara Island (SBI) and Anacapa Island (ANA). Presented here are new field and laboratory data on the ages, paleontology, and sea level history of marine terraces of these two islands. On both islands, the lowest marine terraces have shoreline angle elevations of ~11 m above sea level. …

Promoting Change In Common Tern (Sterna Hirundo) Nest Site Selection To Minimize Construction Related Disturbance., Peter C. Mcgowan, Jeffery D. Sullivan, Carl R. Callahan, William Schultz, Jennifer L. Wall, Diann J. Prosser

United States Geological Survey: Staff Publications

Due to the many challenges facing waterbird populations (Jia et al. 2018, Wetlands International 2018), it has become common practice to limit disturbance to breeding colonies whenever possible to maximize reproductive success. While this may require often unpopular management techniques including beach closures (Jorgensen et al. 2015, Mayo et al. 2015) and predator removal (Neuman et al. 2004, Stocking et al. 2017), such actions are sometimes necessary for the success of the colony. However, there are instances when eliminating disturbance is not possible and birds must be attracted to a new site. A common method for attracting waterbirds to a …

Comparing Structure From Motion Photogrammetry And Computer Vision For Low-Cost 3d Cave Mapping: Tipton-Haynes Cave, Tennessee, Clinton Elmore

Electronic Theses and Dissertations

Natural caves represent one of the most difficult environments to map with modern 3D technologies. In this study I tested two relatively new methods for 3D mapping in Tipton-Haynes Cave near Johnson City, Tennessee: Structure from Motion Photogrammetry and Computer Vision using Tango, an RGB-D (Red Green Blue and Depth) technology. Many different aspects of these two methods were analyzed with respect to the needs of average cave explorers. Major considerations were cost, time, accuracy, durability, simplicity, lighting setup, and drift. The 3D maps were compared to a conventional cave map drafted with measurements from a modern digital survey instrument …

Management Regime And Habitat Response Influence Abundance Of Regal Fritillary (Speyeria Idalia) In Tallgrass Prairie, K. Mccullough, G. Albanese, D.A. Haukos, A.M. Ricketts, S. Stratton

United States Geological Survey: Staff Publications

The >2,570,000-ha Flint Hills ecoregion of Kansas, USA, harbors the largest remaining contiguous tract of tallgrass prairie in North America, a unique system, as the remainder of North America’s tallgrass prairie has succumbed to development and conversion. Consequently, the loss and degradation of tallgrass prairie has reduced populations of many North American prairie-obligate species including the regal fritillary (Speyeria idalia) butterfly. Population abundance and occupied range of regal fritillary have declined >99%, restricting many populations to isolated, remnant patches of tallgrass prairie. Such extensive decline has resulted in consideration of the regal fritillary for protection under the Endangered Species Act. …

Identifying Characteristics Of Actionable Science For Drought Planning And Adaptation, Adam Wilke, Amanda Cravens

Publications of the US Geological Survey

Changing climate conditions can make water management planning and drought preparedness decisions more complicated than ever before. Federal and State natural resource managers can no longer rely solely on historical trends as a baseline and thus are in need of science that is relevant to their specific needs to inform important planning decisions. Questions remain, however, regarding the most effective and efficient methods for extending scientific knowledge and products into management and decision-making. This project analyzed two unique cases of water management to better understand how science can be translated into resource management actions and decision-making, focusing particularly on how …

Detrital Zircon Geochronology Of Paleoproterozoic Sedimentary Rocks From The Upper Huronian Supergroup, Canada, Carolyn M. Hill, Don W. Davis, Patricia L. Corcoran

Western Research Forum

The Huronian Supergroup is a well-known succession of primarily sedimentary rocks exposed north of Lake Huron. Deposition of the succession is constrained between 2450 and 2220 Ma (million years), which corresponds with Earth’s rise of atmospheric oxygen, however the depositional timing of the uppermost formations cannot be refined further due to a lack of interbedded volcanic rocks. A geochronological study of detrital zircon grains from sandstone and claystone beds from the two youngest Huronian formations, the Gordon Lake and Bar River formations, was completed in order to confine the maximum age of deposition.

Zircon is a mineral that commonly forms …

The Antiquity Of The Sahara Desert: New Evidence From The Mineralogy And Geochemistry Of Pliocene Paleosols On The Canary Islands, Spain, Daniel R. Muhs, Joaquín Meco, James R. Budahn, Gary L. Skipp, Juan F. Betancort, Alejandro Lomoschitz

United States Geological Survey: Staff Publications

The Sahara is the largest warm desert in the world, but its age has been controversial, with estimates ranging from Miocene to Holocene. Mineralogical and geochemical data show that paleosols of Pliocene to mid- Pleistocene age on Fuerteventura and Gran Canaria in the Canary Islands have developed in part from inputs of dust from Africa. These paleosols contain quartz and mica, minerals that are abundant in African dust but are rare in the basaltic rocks that dominate the Canary Islands. Trace elements with minimal mobility, Sc, Cr, Hf, Th, and Ta as well as the rare earth elements, show that …

Tropospheric And Ionospheric Anomalies Induced By Volcanic And Saharan Dust Events As Part Of Geosphere Interaction Phenomena, Valerio Tramutoli, Francesco Marchese, Alfredo Falconieri, Carolina Filizzola, Nicola Genzano, Katsumi Hattori, Mariano Lisi, Jann-Yenq Liu, Dimitar Ouzounov, Michel Parrot, Nicola Pergola, Sergey Pulinets

Mathematics, Physics, and Computer Science Faculty Articles and Research

In this work, we assessed the possible relation of ionospheric perturbations observed by Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER), Global Positioning System total electron content (GPS TEC), National Oceanic and Atmospheric Administration (NOAA)-derived outgoing longwave-Earth radiation (OLR), and atmospheric chemical potential (ACP) measurements, with volcanic and Saharan dust events identified by ground and satellite-based medium infrared/thermal infrared (MIR/TIR) observations. The results indicated that the Mt. Etna (Italy) volcanic activity of 2006 was probably responsible for the ionospheric perturbations revealed by DEMETER on 4 November and 6 December and by GPS TEC observations on 4 November and 12 …

Growth, Condition, And Trophic Relations Of Stocked Trout In Southern Appalachian Mountain Streams, Jesse R. Fischer, Thomas J. Kwak, H. Jared Flowers, W. Gregory Cope, Jacob M. Rash, Douglas A. Besler

United States Geological Survey: Staff Publications

Stream trout fisheries are among the most popular and valuable in the United States, but many are dependent on hatcheries to sustain fishing and harvest. Thus, understanding the ecology of hatchery‐reared trout stocked in natural environments is fundamental to management. We evaluated the growth, condition, and trophic relations of Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, and Rainbow Trout Oncorhynchus mykiss that were stocked in southern Appalachian Mountain streams in western North Carolina. Stocked and wild (naturalized) trout were sampled over time (monthly; September 2012–June 2013) to compare condition and diet composition and to evaluate temporal dynamics of trophic …

Notes And Discussion Piece: Status Of The Topeka Shiner In Iowa, Clay L. Pierce, Nicholas T. Simpson, Alexander P. Bybel, Courtney L. Zambory, Michael J. Weber, Kevin J. Roe

United States Geological Survey: Staff Publications

The Topeka shiner Notropis topeka is native to Iowa, Kansas, Minnesota, Missouri, Nebraska, and South Dakota and has been federally listed as endangered since 1998. Our goals were to determine the present distribution and qualitative status of Topeka shiners throughout its current range in Iowa and characterize the extent of decline in relation to its historic distribution. We compared the current (2016–2017) distribution to distributions portrayed in three earlier time periods. In 2016–2017 Topeka shiners were found in 12 of 20 HUC10 watersheds where they occurred historically. Their status was classified as stable in 21% of the HUC10 watersheds, possibly …

Suspended Sediment Transport Revealed By Patterns In Turbidity And Electrical Conductivity Curves In Three Cave Systems In Missouri, Usa., Caroline M. Mierzejewski

LSU Master's Theses

In cave streams, the movement of sediment as suspended and bed loads are linked to the occurrence of precipitation events on the surface. During precipitation events, the discharge of the streams in the basin increases. As those surface streams flow into cave streams via sinkholes or fissures, the discharge in cave streams increase. In addition to changes in discharge, the response of the surface and cave streams to precipitation include changes in turbidity and electrical conductivity of the stream water.

Changes in turbidity (Tu), electrical conductivity (EC), and discharge (Q) of water in the cave stream can be used to …

Flow Alteration-Ecology Relationships In Ozark Highland Streams: Consequences For Fish, Crayfish And Macroinvertebrate Assemblages, Dustin T. Lynch, Douglas R. Easure, Daniel D. Magoulick

United States Geological Survey: Staff Publications

We examined flowalteration-ecology relationships in benthic macroinvertebrate, fish, and crayfish assemblages in Ozark Highland streams, USA, over two years with contrasting environmental conditions, a drought year (2012) and a flood year (2013). We hypothesized that: 1) there would be temporal variation in flow alteration-ecology relationships between the two years, 2) flow alteration-ecology relationshipswould be stronger during the drought year vs the flood year, and 3) fish assemblages would show the strongest relationships with flow alteration. We used a quantitative richest-targeted habitat (RTH) method and a qualitative multihabitat (QMH) method to collect macroinvertebrates at 16 USGS gaged sites during both years. …

Flow Alteration-Ecology Relationships In Ozark Highland Streams: Consequences For Fish, Crayfish And Macroinvertebrate Assemblages, Dustin Thomas Lynch, Douglas R. Leasure, Daniel D. Magoulick

United States Geological Survey: Staff Publications

We examined flowalteration-ecology relationships in benthic macroinvertebrate, fish, and crayfish assemblages in Ozark Highland streams, USA, over two years with contrasting environmental conditions, a drought year (2012) and a flood year (2013). We hypothesized that: 1) there would be temporal variation in flow alteration-ecology relationships between the two years, 2) flow alteration-ecology relationshipswould be stronger during the drought year vs the flood year, and 3) fish assemblages would show the strongest relationships with flow alteration. We used a quantitative richest-targeted habitat (RTH) method and a qualitative multihabitat (QMH) method to collect macroinvertebrates at 16 USGS gaged sites during both years. …

Seismic Landslide Hazard Mapping For Greater Vancouver, British Columbia, Ali Fallah Yeznabad, Sheri E. Molnar, Hesham M. El Naggar

Western Research Forum

The lower Mainland of southwest British Columbia (BC) hosts about 3.5 million people and significant infrastructures of national importance. Southwestern BC has the highest seismic risk in Canada with significant potential to cause earthquake-induced hazards including tsunamis, liquefaction and landslides. A Cascadia mega-thrust (M_W 9) earthquake is predicted to generate $75 billion Canadian dollars in losses. This damage can be resulted from ground shaking or its secondary phenomena like landslides; ground shaking during earthquakes may trigger landslides that can damage or destroy buildings, bury roads and highways and kill and injure people. In Canada, during the past century and …

Newgeochemical Evidence For The Origin Of North America's Largest Dune Field, The Nebraska Sand Hills, Central Great Plains, Usa, Daniel R. Muhs, James R. Budahn

United States Geological Survey: Staff Publications

The Nebraska SandHills region is the largest dune field inNorthAmerica and has diverse aeolian landforms. It has been active during both the late Pleistocene and late Holocene. Despite decades of study, the source of sediment for this large sand sea is still controversial. Here we report new trace element compositions of aeolian sand that are compared to four hypothesized sediment sources, Tertiary rocks of the Arikaree Group and Ogallala Group, unconsolidated sands of Pliocene age, and Platte River systemsands. All four potential sources have amineralogy that is similar to the Nebraska Sand Hills. K/Rb, K/Ba, Sc-Th-La, Eu/Eu*, LaN/YbN, As/Sb, and …

The Impact-Generated Hydrothermal System Of The East Clearwater Lake Impact Structure, Quebec, Canada, Derek King

Electronic Thesis and Dissertation Repository

Alteration mineralization at impact craters gives insight into the hydrothermal system generated post-impact. This is the first work to document the alteration mineralization to characterize the East Clearwater impact-generated hydrothermal system. The East Clearwater hydrothermal system in the impact melt rocks and melt-bearing breccias transitions from zeolite-smectite assemblages to chlorite-dominant assemblages with depth. pH evolution of the East Clearwater impact-generated hydrothermal system reflects magmatic-driven hydrothermal systems in granitic rocks. West Clearwater has a different alteration style. Given an impact forms a hydrothermal system, the style of alteration will not only vary dependent on target lithologies (i.e., crystalline, sedimentary, mixed target), …

Stable Isotopes Of Clay Minerals From Autoclave Tests Of Oil Sands: Implications For Clay Formation During Steaming Of Alberta Clearwater Oil Sands, Shaoneng He, Fred J. Longstaffe, Zhihong Zhou

Earth Sciences Publications

In an effort to evaluate mineral-water isotopic exchange during cyclic steam stimulation (CSS), solutions and<2 μm berthierine-dominated solids from the Clearwater Formation oil sands of Alberta, Canada were analyzed for stable isotope compositions before and after reaction in autoclaves for 1008 h at 250 °C. There was no significant change in solution δ¹⁸O and δ²H, which is consistent with the high water/mineral ratio used in the experiments. The solids showed a marked decrease in both δ¹⁸O and δ²H following the experiments. Pre-run solids have δ¹⁸O of +9.5 to +12.9‰and …

Assessment Of Chronic Low-Dose Elemental And Radiological Exposures Of Biota At The Kanab North Uranium Mine Site In The Grand Canyon Watershed, Danielle Cleveland, Jo Ellen Hinck, Julia S. Lankton

United States Geological Survey: Staff Publications

High-grade U ore deposits are in various stages of exploitation across the Grand Canyon watershed, yet the effects of U mining on ecological and cultural resources are largely unknown. Wecharacterized the concentrations of Al, As, Bi, Cd, Co, Cu, Fe, Pb, Hg, Mo, Ni, Se, Ag, Tl, Th, U, and Zn, gross alpha and beta activities, and U and Th radioisotopes in soil, vegetation (Hesperostipa comata, Artemisia tridentata, Tamarix chinensis), and rodents (Peromyscus maniculatus, P. boylii) to waste material at the Kanab North mine, a mine with decades-long surficial contamination, and compared the concentrations (P<0.01) to those at a premining site (Canyon Mine). Rodent tissues were also analyzed for radium-226 and microscopic lesions. Radioactivities and some elemental concentrations (e.g., Co, Pb, U) were greater in the Kanab North mine biological samples than in Canyon Mine biota, indicating a mining-related elemental signature. Mean rodent Ra-226 (111 Bq/kg dry weight [dry wt]) was 3 times greater than expected, indicating radioactive disequilibrium. Multiple soil sample U concentrations exceeded a screening benchmark, growth inhibition thresholds for sensitive plants, and an EC20 for a soil arthropod. Lesions associated with metals exposure were also observed more frequently in rodents at Kanab North than those at Canyon Mine but could not be definitively attributed to U mining. Our results indicate that Kanab North biota have taken up U mining-related elements owing to chronic exposure to surficial contamination. However, no literature-based effects thresholds for small rodents were exceeded, and only a few soil and vegetation thresholds for sensitive species were exceeded; therefore, adverse effects to biota from U mining-related elements at Kanab North are unlikely despite chronic exposure.

Chaco Canyon, New Mexico: A Caretaker City And A Pilgrimage Destination, Larry Benson, Deanna N. Grimstead, John R. Stein, David A. Roth, Terry I. Plowman

United States Geological Survey: Staff Publications

Some Southwestern archaeologists continue to ascribe to the hypothesis that Chaco was agriculturally productive to the point that it could support at least a few thousand full-time residents. This paper suggests an alternative hypothesis; i.e., Chaco was marginally productive and could only support a few hundred permanent residents. Isotopic analysis of mammal teeth found in trenches cut through platform mounds fronting Pueblo Bonito indicate the possibility that much of the meat consumed by Chacoan residents and visitors came from higher elevation sites bordering the San Juan Basin. We suggest that resident population estimates based on great house room numbers and …

Coastal Wetlands: A Synthesis, Charles S. Hopkinson, Eric Wolanski, Mark M. Brinson, Donald R. Cahoon, Gerardo M.E. Perillo

United States Geological Survey: Staff Publications

What are coastal wetland ecosystems, what are their limits of distribution, and where do they exist in the overall coastal landscape? There are several general definitions for wetlands, but the Ramsar definition is likely the most broadly encompassing (http://www.ramsar. org/), whereas others are more focused definitions tailored to country-specific protection and management policies (Mitsch and Gosselink, 2006). We offer a very general approach rather than a precise definition: coastal wetlands are ecosystems that are found within an elevation gradient that ranges between subtidal depths where light penetrates to support photosynthesis of benthic plants to the landward edge where the sea …

Promoting Change In Common Tern (Sterna Hirundo) Nest Site Selection To Minimize Construction Related Disturbance., Peter C. Mcgowan, Jeffery D. Sullivan, Carl R. Callahan, William Schultz, Jennifer L. Wall, Diann J. Prosser

United States Geological Survey: Staff Publications

Due to the many challenges facing waterbird populations (Jia et al. 2018, Wetlands International 2018), it has become common practice to limit disturbance to breeding colonies whenever possible to maximize reproductive success. While this may require often unpopular management techniques including beach closures (Jorgensen et al. 2015, Mayo et al. 2015) and predator removal (Neuman et al. 2004, Stocking et al. 2017), such actions are sometimes necessary for the success of the colony. However, there are instances when eliminating disturbance is not possible and birds must be attracted to a new site. A common method for attracting waterbirds to a …

Response Of Vegetation In Open And Partially Wooded Fens To Prescribed Burning At Seney National Wildlife Refuge, Jane E. Austin, Wesley E. Newton

Publications of the US Geological Survey

The health and function of northern peatlands, particularly for fens, are strongly affected by fire and hydrology. Fens are important to several avian species of conservation interest, notably the yellow rail (Coturnicops noveboracensis). Fire suppression and altered hydrology often result in woody encroachment, altering the plant community and structure. Woody encroachment and its effects on biodiversity have become an increasing concern in the conservation and management of plant communities. This study evaluated the effects of spring and summer prescribed burns on the plant community, cover, and structure in open and partially wooded fens at Seney National Wildlife Refuge, Michigan, using …

Flood-Inundation Maps For The North Platte River At Scottsbluff And Gering, Nebraska, 2018, Kellan R. Strauch

Publications of the US Geological Survey

Digital flood-inundation maps for an 8.8-mile reach of the North Platte River, from 1.5 miles upstream from the Highway 92 bridge to 3 miles downstream from the Highway 71 bridge in Scottsbluff County, were created by the U.S. Geological Survey (USGS) in cooperation with the Cities of Scottsbluff and Gering, Nebraska. The flood-inundation maps, which can be accessed through the Flood Inundation Mapping (FIM) Program website at https://www.usgs.gov/mission-areas/water-resources/science/flood-inundation-mapping-fim-program?qt-science_center_objects=0#qt-science_center_objects, depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage on the North Platte River at Scottsbluff, Nebr. (station number 06680500). Near-real-time …

Identifying Key Factors Affecting Translational Landslides In Part Of The Yakima Fold And Thrust Belt, Washington State, Joseph Schilter

All Master's Theses

Washington has one of the fastest growth rates in the nation, and unfortunately also is among the most landslide-prone states. With increased population density and urban sprawl, the need for landslide hazard assessment grows. On the Columbia Plateau in central Washington, the smooth rigid, inclined surfaces of the Columbia River Basalts (CRBs) with loose sediment layers between them induces landslides of large blocks of bedrock. These hazards remain poorly understood, but their significance was heightened by the 2017 Rattlesnake Hills Landslide that currently threatens a community and an interstate highway south of Yakima, Washington. I propose that the strongest influences …

Spatial Conservation Planning Under Uncertainty: Adapting To Climate Change Risks Using Modern Portfolio Theory, Mitchell J. Eaton, Simeon Yurek, Zulqarnain Haider, Julien Martin, Fred Johnson, Bradley J. Udell, Hadi Charkhgard, Changhyun Kwon

United States Geological Survey: Staff Publications

Climate change and urban growth impact habitats, species, and ecosystem services. To buffer against global change, an established adaptation strategy is designing protected areas to increase representation and complementarity of biodiversity features. Uncertainty regarding the scale and magnitude of landscape change complicates reserve planning and exposes decision makers to the risk of failing to meet conservation goals. Conservation planning tends to treat risk as an absolute measure, ignoring the context of the management problem and risk preferences of stakeholders. Application of risk management theory to conservation emphasizes the diversification of a portfolio of assets, with the goal of reducing the …

Prehistoric Chaco Canyon, New Mexico: Importation Of Meat And Maize, Larry Benson, Deanna Grimstead, John R. Stein, David A. Rith, Terry L. Plowman

United States Geological Survey: Staff Publications

In a recent paper, Benson and Grimstead (2019) determined that only minimal amounts of maize could have been grown in Chaco Canyon due to its aridity, short growing season, and frequent summer flooding of the valley floor. In this paper it is shown that deer and rabbit densities within semiarid regions such as the Canyon are such that 2300 Canyon residents would eliminate essentially all small and large mammals within a year. This implies that food (meat and maize) must have been imported from one or more outlying areas to feed the Canyon's residential population. This would have entailed ~18,000 …