Age Of The Artifact-Bearing Deposit
In comparison with similar soils dated elsewhere in arid and semiarid regions, the relict paleosol on the Yermo Fan itself is judged to be at least as old as Stage 5 of the marine oxygen-isotope stage chronology, about 80,000 to 125,000 b.p. The underlying artifact-bearing Yermo deposits were probably laid down during a preceding epoch of regional alluviation, probably Stage 6, about 125,000 to 200,000 b.p. (Bischoff et al. 1981; Shlemon and Budinger 1990).
Thermoluminescence analysis of a sample comprised of moderate and fine sands and silts taken from a depth of 5 m in Master Pit I yielded an age of 135,000 +infinity/-30,000 years. (Debenham 1999).
Uranium-thorium (U-Th) dating of laminar calcium carbonate rinds encrusting artifacts and other clasts in the basal deposits yielded an average age of approximately 200,000 years. This age was replicated in separate analyses performed more than ten years apart. The carbonate rinds of groundwater origin were probably precipitated during, or shortly after, deposition of the basal mudflows.