A Study of Bedrock Strength Controls on the Erosion of the Colorado Plateau

There has been renewed debate over the mechanisms of uplift and erosion in the Colorado Plateau, and in order to understand the patterns of topography and process in this landscape a third factor of bedrock properties must be considered. Our goal is to compile a dataset of bedrock strength and explore it in the context of topographic metrics. To do so, a methodology problem must be addressed. Traditional rock-strength measures such as Schmidt hammer rebound, Selby rock-mass strength, or tensile strength ignore weak rock types. We hope to develop an indirect, topography-based method that reliably estimates the strength of mud-rocks that are too incompetent to test directly. We will complete measurements of the characteristics of rock formations along the Colorado and Green rivers to allow erosional resistance to be quantified. The drainage in the Colorado Plateau can be broken up into 48 reaches underlain by a variety of bedrock compositions including quartzite, sandstone, shale, limestone, evaporites, and crystalline basement. Compressive strength data from most of the outcropping rock formations have been collected from all reaches, however tensile strength data for these rocks are incomplete, and there are no data from any incompetent rocks. Our existing data indicate there are strong relations between rock strength and channel/valley width and gradient and stream power. Documentation will be done to complete modified Selby rock mass strength evaluations, noting thickness and proportion of beds that are too weak to be tested. From these new data, we aim to back-calculate strength of “weak” beds using functional relations between measured channel widths and known rock strengths, similar to previous numerical modeling in the region

Linkages of fluvial terrace formation and geometry to Milankovitch-scale climate change revealed by the chronostratigraphy of the Colorado River above Moab, UT, and regional correlations

The Colorado River flows from its Rocky Mountain headwaters to the Gulf of California, draining most of the Colorado Plateau. Although the river’s hydrology is set in the Rockies, its sediment load is largely supplied by the plateau drylands of the lower drainage. Terrace genesis at Milankovitch timescales • Reflects changing dynamics between fluctuating hydrology and local sediment supply? • Relations to major late Pleistocene climate shifts? • Do study terraces correlate regionally? (i.e. are pulses of sedimentation transient or synchronous?) • What controls the formation of fill vs. strath terraces? Deformation of terraces • Is there a detectable influence of salt tectonism on terrace form and type? Our goal is to address these questions through detailed chronostratigraphy, correlation, surveying, and long-profile analysis

Active salt deformation and rapid, transient incision along the Colorado River near Moab, Utah

In certain settings, erosion is driven by and balanced with tectonic uplift, but the evolution of many landscapes is dominated by other factors such as geologic substrate, drainage history, and transient incision. The Colorado Plateau is an example where these controls are debated and where salt deformation is hypothesized to be locally active and driven by differential unloading, although this is unconfirmed and unquantified in most places. We use luminescence-dated Colorado River terraces upstream of Moab, Utah, to quantify rates of salt-driven subsidence and uplift at the local scale. Active deformation in the study area is also supported by patterns of concavity along tributary drainages crossing salt structures. Subsidence in Professor Valley at a time-averaged rate of _500 m/Myr (meters/million years) is superimposed upon rapid bedrock incision rates that increase from _600 to _900 m/Myr upstream through the study area. Such high rates are unexpected given the absence of sources of regional tectonic uplift here. Instead, the incision rate pattern across the greater area is consistent with a transient signal, perhaps still from ancient drainage integration through Grand Canyon far downstream, and then amplified by unloading at both the broad regional scale and at the local canyon scale. ©2015. American Geophysical Union. All Rights Reserved

Grand Canyon as a Universally Accessible Virtual Field Trip for Intro Geoscience Classes Using Geo-Referenced Mobile Game Technology

There is a well-documented and nationally reported trend of declining interest, poor preparedness, and lack of diversity within U.S. students pursuing geoscience and other STEM disciplines. We suggest that a primary contributing factor to this problem is that introductory geoscience courses simply fail to inspire (i.e. they are boring). Our experience leads us to believe that the hands-on, contextualized learning of field excursions are often the most impactful component of lower division geoscience classes. However, field trips are becoming increasingly more difficult to run due to logistics and liability, high-enrollments, decreasing financial and administrative support, and exclusivity of the physically disabled. Recent research suggests that virtual field trips can be used to simulate this contextualized physical learning through the use of mobile devices – technology that exists in most students’ hands already. Our overarching goal is to enhance interest in introductory geoscience courses by providing the kinetic and physical learning experience of field trips through geo-referenced educational mobile games and test the hypothesis that these experiences can be effectively simulated through virtual field trips. We are doing this by developing “serious”ù games for mobile devices that deliver introductory geology material in a fun and interactive manner. Our new teaching strategy will enhance undergraduate student learning in the geosciences, be accessible to students of diverse backgrounds and physical abilities, and be easily incorporated into higher education programs and curricula at institutions globally. Our prototype involves students virtually navigating downstream along a scaled down Colorado River through Grand Canyon – physically moving around their campus quad, football field or other real location, using their smart phone or a tablet. As students reach the next designated location, a photo or video in Grand Canyon appears along with a geological question. The students must answer each question correctly in order to proceed to the next location and accrue points in the game and multiple attempts reduce the number of points earned when the correct answer is found. The questions are either multiple choice or involve touch-screen interaction to identify a specific geologic feature. Initial testing of the prototype game in Historical and Physical geology courses at Utah State University indicate that students enjoy the mobile “exploration”ù nature of the game as well as experiencing photographs of geologic features rather than traditional cartoons. Qualitative evaluation using anonymous surveys was conducted to help determine the usability of the game and the potential effectiveness of this technology-based approach. Students were asked about the degree of fun and difficulty of the game, content learned, and their overall response to features they liked/disliked about it. The results of these early assessments are positive, both in regard to the improvement of students’ understanding of key geology concepts and their enjoyment of learning with the technology in a mobile orienteering manner. This is a positive first step in an innovative teaching tool with the power to overcome the pervasive problem of the boring first year STEM course and make world-class field trips accessible to all

Assessment of Student Learning Using Augmented Reality Grand Canyon Field Trips for Mobile Smart Devices

In searching for ways to improve undergraduate success in introductory geoscience courses, the importance of experiential learning in engaging students has become clear—and in geoscience, that is encapsulated best by field trips. However, as general education class sizes increase, so do the cost, liability, and difficulty of running a field trip. A solution for economically and conveniently bringing kinesthetic field experiences to a broader audience lies in the integration of technology through mobile-device games, apps, and augmented reality (AR) field trips. We report here an examination of learning gains at five colleges after intervention with augmented reality field trips to Grand Canyon. The AR field trips cover three topics taught in introductory geoscience courses: geologic time, geologic structures, and hydrologic processes. Results involving nearly 1000 students show that overall gains are similar to control groups, with completion of the AR field trips being a predictor of student learning success in some cases. Prior interest in the geosciences, students’ base-level understanding of the material, and whether or not the student is a science, technology, engineering, and mathematics (STEM) major are strong predictors of improvement in geoscience learning. Gender and ethnicity had no statistical impact on the results, suggesting the AR field trip modules have broad reach across student demographics. Because these modules have been shown elsewhere to increase student interest in learning the geosciences, we advocate their adoption, leading to increases in student learning

Sandstones and Utah’s canyon country: Deposition, diagenesis, exhumation, and landscape evolution

South-central Utah’s prominent sandstones and deeply dissected landscapes are the focus of this four-day trip, which begins and ends in Grand Junction, Colorado. Studies of the apatite grains in sandstones adjacent to igneous intrusions are revealing new information on the timing and rate of Cenozoic erosion. Iron-oxide-cemented concretions in other rocks record how reduced-iron carbonates and subsurface microbes interacted when near-surface, oxygenated waters started to flush the reducing, CO2-rich waters from Colorado Plateau aquifers. New geochronologic techniques that are being applied to the plateau rocks have the potential to expand our knowledge of how diagenetic episodes relate to the evolving topography of this classic geologic setting

Reply to Simon and Reed: Independent and Converging Results Rule Out Historic Disturbance and Confirm Age Constraints for Barrier Canyon Rock Art

We welcome this further discussion of our results on the age of the Great Gallery rock art in the Canyonlands of Utah. The comment by Simon and Reed (1) focuses on just one of the three components of our study (2), which is presented in greater technical detail in ref. 3 and is surely our best-constrained and least-surprising result: the dating of a rock-fall that removed some of the art and thus provides a minimum age. Simon and Reed (1) point out that the Great Gallery panel is not pristine and relate the sordid human history of visitation and possible disturbance to the site. Indeed, being aware of this during our research, one of our initial hypotheses was that the rock fall may be historic. Despite the possibility of recent disturbance to some of the talus boulders, our results document that the rock fall occurred ∼900 y ago, and for the boulder we sampled a scenario of historic disturbance and exposure such as postulated by Simon and Reed (1) can be ruled out

Age of Barrier Canyon-style rock art constrained by cross-cutting relations and luminescence dating techniques

Rock art compels interest from both researchers and a broader public, inspiring many hypotheses about its cultural origin and meaning, but it is notoriously difficult to date numerically. Barrier Canyon-style (BCS) pictographs of the Colorado Plateau are among the most debated examples; hypotheses about its age span the entire Holocene epoch and previous attempts at direct radiocarbon dating have failed. We provide multiple age constraints through the use of cross-cutting relations and new and broadly applicable approaches in optically stimulated luminescence dating at the Great Gallery panel, the type section of BCS art in Canyonlands National Park, southeastern Utah. Alluvial chronostratigraphy constrains the burial and exhumation of the alcove containing the panel, and limits are also set by our related research dating both a rockfall that removed some figures and the rock’s exposure duration before that time. Results provide a maximum possible age, a minimum age, and an exposure time window for the creation of the Great Gallery panel, respectively. The only prior hypothesis not disproven is a late Archaic origin for BCS rock art, although our age result of A.D. ∼1–1100 coincides better with the transition to and rise of the subsequent Fremont culture. This chronology is for the type locality only, and variability in the age of other sites is likely. Nevertheless, results suggest that BCS rock art represents an artistic tradition that spanned cultures and the transition from foraging to farming in the region. Archaeology is focused upon material records, contextualized in time. Rock art is a record with the potential to provide unique insight into the dynamics and evolution of culture, but it generally lacks stratigraphic or chronologic context. Interpretation of the origin and meaning of rock art is indirect at best, or simply speculative. In the case of some pictographs, pigments may include or have enough accessory carbon for accelerator mass spectrometry (AMS) radiocarbon dating (1⇓⇓–4). In other special situations, such as caves, minimum age constraints have been obtained by various techniques of dating material that overlies or entombs rock art (5⇓–7). However, most rock art remains undatable and researchers rely upon stylistic comparison and indirect associations with artifacts at nearby sites (8, 9). The case in point for this study is arguably the most compelling and debated rock art in the United States—the Barrier Canyon style (BCS) of the Colorado Plateau. Previous attempts to derive an absolute chronology have failed and its age remains unknown, with widely ranging hypotheses that have remained untested until now. The continued development of dating techniques offers new possibilities for hypothesis testing. The optically stimulated luminescence (OSL) signals from mineral grains make it possible to date the deposition of most sediment that is exposed to a few seconds of full sunlight before burial, and its use in the earth and cultural sciences has greatly increased (10, 11). Among the latest applications of OSL are techniques dating the outer surfaces of rock clasts that have become shielded from light, including those with archaeological context (12⇓⇓–15). Recent work has furthermore used the “bleaching” profile of decreasing luminescence signal toward the surface of rock to estimate exposure time to sunlight (16, 17). Using these dating tools, we can constrain the age of rock art and gain new insight into past cultures and landscapes. Here, we synthesize results from three approaches to dating the type section of BCS art, the Great Gallery in Canyonlands National Park of southeastern Utah. Through dating the full alluvial stratigraphy and a rockfall event that both have incontrovertible cross-cutting relations with the rock art, and then by determining the exposure duration of a painted rock surface, we greatly narrow the window of time when the rock art was created. These approaches do not require direct sampling of rock art and have strong potential for application to other archaeological and surface processes research. Although our results are only for the type section of BCS art, and chronological variability should be expected for the style across the region, they suggest that BCS art coincides with the transition to agriculture in the northern Colorado Plateau and may not have been limited to a specific archaeological culture