NEW RECORDS OF FRESHWATER FISH FROM IRVINGTONIAN DEPOSITS AROUND THE SALTON TROUGH, SOUTHERN CALIFORNIA AND NORTHWESTERN SONORA, MEXICO

The El Golfo Badlands are located in the northwestern part of Sonora, Mexico. Although the El Golfo was collected as early as 1938 by Chester Stock of California Institute of Technology, the last 15 years, staff and volunteers from Reserva de la Biosfera–Alto Golfo de California y Delta del Rio Colorado (SMERNAP), Arizona Western College, and George C. Page Museum have made a concerted effort to survey exposures of Pleistocene-age Colorado River delta sediments for paleontological resources. Although the age of the El Golfo deposits is not well known, the fossil mammalian fauna correlates with the Irvingtonian -age section of the Anza Borrego Desert State Park stratigraphic sequence. At El Golfo, more than 3500 mapped vertebrate localities have yielded over 66 genera. In addition to the larger vertebrate fossils, several new microvertebrate localities have been identified. In conjunction with this work, the field survey and microvertebrate locality work, a small number of bony fish remains have been recovered. The bony fish remains consist primarily of isolated bones, teeth and vertebrae. At least three species of Colorado River fishes represented; razorback sucker (Xyrauchen texanus), pike minnow (Ptychocheilus lucius), chub (Gila).

Recently, paleontologists from the Department of Paleontology of the San Diego Natural History Museum (SDNHM) monitored ground disturbing activities during construction of the San Diego Gas and Electric Company Sunrise Powerlink Transmission Line for paleontological resources in western Imperial County, California. Near Seeley, at one of the tower locations, fossil-bearing fine-grained sediments of the Irvingtonian Brawley Formation , remains of at least four kinds of freshwater fish were recovered (Gila-chub, Xyrauchen texanus-razorback sucker, Gasterosteus aculeatus-threespine stickleback and a very small bony fish). Today, the threespine stickleback is not present in drainages the Salton Trough nor Colorado River. There are several possible explanations for this occurences