THE GILCREASE RANCH MAMMOTH SITE, LAS VEGAS VALLEY

The northwestern Las Vegas Valley is rich in the fossil remains of Late Pleistocene Columbian mammoths (Mammuthus columbi). One particularly rich site is a pluvial spring deposit on the Gilcrease Ranch. Some of this material has been excavated and is currently housed in private collections, while some material remains in situ. A small number of archaeological artifacts have been found with these fossils, but no unequivocal relationship has yet been demonstrated between the artifacts and mammoth fossils. Together with the nearby Tule Springs site (Rancholabrean), the Gilcrease mammoth site presents an excellent opportunity to address paleoecological questions concerning Late Pleistocene mammoths in this area. A significant portion of the fossil material comprises teeth. Some Proboscideans, including mammoths, grow six successive sets of teeth in their lifetime. This trait allows the age of each animal at the time of death to be determined by comparison to dentition models from extant Proboscidean taxa. Sites with an abundant fossil record of Proboscidean teeth age profiles may be constructed for the population reflected in the death assemblage.

The age profile of the Gilcrease Ranch mammoth population lacks juveniles and older adults. Preliminary analyses of this distribution appear to indicate an environmentally stressed population. However, since these fossils are in a spring deposit that was agitated by spring flow, no useful stratigraphy exists for correlation. It is not yet clear whether the Gilcrease Ranch mammoth teeth represent a single population preserved during a short time interval or a slow accumulation of individuals over several thousands of years. Application of ¹⁴C dating methods to these fossil mammoth teeth will allow tighter constraints to be placed on the population dynamics of Rancholabrean age mammoths in the southern Basin and Range.