Compilation, Calibration, and Synthesis of Faunal and Floral Radiocarbon Dates, Rancho La Brea, California

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This paper presents a compilation and synthesis of calibrated radiocarbon dates for the Rancho La Brea tar pits, Los Angeles, California. A literature survey yielded 188 dates, and 21 additional dates are presented here for the first time. These range in age from 185 to 50,000 radiocarbon years. Dating of Rancho La Brea fossils has been uneven; only from Pits 91 and 2051 have more than 30 dates been obtained. The depositional history of well-sampled pits was complex, with one or more episodes of major accumulation interspersed with lower background levels of entrapment. The most significant quantifiable source of error of Rancho La Brea 14C dates is calibration error. Dates younger than 21,381 radiocarbon years can be calibrated using the IntCal04 calibration curve and yield an accurate estimate of age. Most older dates cannot be accurately calibrated at this time. Calibration of radiocarbon dates is important because raw radiocarbon dates consistently underestimate calendar dates, usually by several thousand years.


This article first appeared in the December 2009 issue of Contributions in Science, the member magazine of the Natural History Museum of Los Angeles County, and is reprinted with permission.

©2009 Natural History Museum of Los Angeles County