The Upper Miocene Barstow Formation crops out in the western Mojave Desert. In the southern Calico Mountains, green petroliferous shale beds of the Barstow Formation contain calcareous nodules from which silicified organisms can be recovered by acid etching. Reconstruction of the physical environment during the time of deposition of the fossil-bearing beds is made by comparing the insects of the Miocene fauna with their modern analogs. The Barstow Formation in this area was deposited in a fairly large, warm lake whose waters were rich in dissolved minerals. Periodically the lacustrine environment was disturbed in a way which resulted in the death and preservation of many soft-bodied organisms. The Miocene lake was surrounded by grassy plains and upland areas supporting a rassy woodland. The climate of the region was semiarid with hot summers and mild winters.

End_of_Article - Last_Page 949------------