Remnants of sedimentary basin levels in southeastern Arizona are prominent and striking deposits, and as such they have attracted the attention of geologists from the early 20th century through the present. Despite extensive descriptive work capturing their visual conspicuousness, there is little consensus on the ages or geologic origins of these deposits. Although the sediments with which these landforms were built have obvious source areas that can be traced and mapped, the potential combinations of tectonic and climatic forces conspiring to leave such deposits abandoned are far from clear and have not been well examined. The ages inferred for loosely correlative basin high stands have ranged from ~20,000 years ago to 1.0-2.2 Ma and are based more on conjecture than quantitative geochronology. This project will establish an absolute timeline for the final stages of when these basin were filled with sediments, as well as when the basins were subsequently incised and dissected by regional erosional events. Establishing such a timeline requires application and development of cosmogenic nuclide methodology that will extend its temporal reach and test the innovative use of multiple stable and radio-nuclides. The sampling strategy will cover a broad range of sedimentary basin levels across southeast Arizona and will quantify both the ages of the deposits and the source area erosion rates. Because the undeformed basin high stand surfaces and underlying basin fill may date to the time that active tectonic forcing ceased in the region, the erosion of the surfaces is likely to have been driven by climatic forcing. Firmly establishing the chronology of these features, as well as the paleo-erosion rates of the source areas thus helps to build a bridge in understanding between how tectonic and climatic forces shape the Earth's surface.

The visually arresting nature of these surfaces across southeastern Arizona insures broad interest in their origins as well as how they may enable insight into tectonic and climatic forces. By establishing the geochronology of such widely studied and virtually undated landscapes we will expand the intellectual reach of this project well beyond the testing of hypotheses. Specifically, the Sky Island Alliance will help us coordinate how understanding the impacts of past climates on the landscape will help better predict future changes across the ecologically sensitive areas of this study. Each of the sedimentary deposits that we are studying originates in source area that is now home to endemic species and spatially isolated ecosystems. There is, therefore, interdisciplinary interest in quantitatively understanding how these landscapes change under different climate regimes. Additionally, the NSF-funded Jemez River Critical Zone Observatory (CZO), run by colleagues at the University of Arizona, has field sites near some of our field sites. We are coordinating field efforts and dating strategies with them, thus insuring synergy between projects with intellectual overlap, but very different project objectives. We will coordinate training and outreach of undergraduate and K-12 students with both collaborators, thus further widening the reach of the project. Collaborative research between this project and the Berkeley Geochronology Center will help develop facilities at Arizona State University as well as train graduate students. Finally, class trips to the field areas used for this project are helping to develop both the field component and the curriculum of undergraduate and graduate courses taught in our school.