The late Cenozoic history of surface waters in the southwestern Great Basin and lower Colorado River region has been a subject of intensive study for more than 200 years. Prior models of regional drainage history have been undergoing major revision in the past decade as a result of more refined studies of the lacustrine and fluvial rock records and improved dating methods. At the same time, a substantial body of pertinent evidence has been rapidly accumulating in the form of biogeographic inquiries of diverse aquatic organisms that are based on detailed examination of the fossil record, phylogenetic analysis, phylogeography, and other modern analytical tools. The abstracts in this volume represent presentations from a workshop held in April 2005 at the Desert Studies Center in Zzyzx, California, in which these geologic and biotic perspectives were summarized and integrated to provide a current synthesis of the aquatic history of this fascinating western North American region. Abstracts by U.S. Geological Survey authors were reviewed and approved prior to presentation, whereas abstracts by authors outside the U.S. Geological Survey were reviewed and in some cases slightly revised following the workshop.
Key issues addressed in the workshop include the following: (1) The configuration, areal extent, and temporal development of the chain of inter-connected lakes which emptied into Death Valley during periods of the Pleistocene. (2) The development of Mojave River drainage in conjunction with uplift of the Transverse Ranges and downstream integration of progressively lower basins. (3) The late Cenozoic history of drainage in the lower Colorado River region prior to the incision of Grand Canyon, including the possible existence of an inland estuarine embayment of the ancestral Gulf of California. (4) Comparison of the biogeographic histories of regional aquatic organisms. Reconciling differences in patterns with factors such as ecological deployment, modes of dispersal, and biogeographic origin. Correlating patterns with current interpretations of drainage history based on the physical record and seeking explanations for major discrepancies.
The workshop, sponsored by the U.S. Geological Survey Earth Surface Dynamics Program and National Cooperative Geologic Mapping Program and by the Smithsonian Institution, was open to all scientists interested in the hydrographic history of the southwestern Great Basin and lower Colorado River regions. Participants included research scientists in geology, paleontology, and biology from the U.S. Geological Survey, Smithsonian Institution, California State Parks and Fish and Game Departments, the Desert Research Institute, Arizona Geological Survey, Nevada Bureau of Mines and Geology, 17 universities throughout the United States and one in Canada, and private consultants. The meeting also was attended by managers from the Mojave National Preserve. The workshop included a series of presentations that reviewed major ideas concerning regional hydrographic history and summarized past and present studies from the geologic and biotic perspectives, followed by presentations of new and provocative ideas and research thrusts. The meeting encouraged geologists and biologists to interact to develop a broader perspective on the types of research that are being conducted to address issues of regional drainage history. The convenors hope that these new opportunities of interaction among scientists of different disciplines will lead to future proposals for collaborative studies.