Revised age of the Rockland tephra, northern California: Implications for climate and stratigraphic reconstructions in the western United States: Reply: REPLY

Sarna-Wojcicki suggests that the ⁴⁰Ar/³⁹Ar age of 614 ± 8 ka for the Rockland tephra (Lanphere et al., 1999) is too old because of the presence of xenocrystic plagioclase. The Rockland tephra is indeed full of lithic debris that can be seen at any well-exposed outcrop of ash-flow or air-fall deposits. In order to minimize contamination, we selected pumice lumps known to be representative of the Rockland magma. Plagioclase in the pumice lumps forms a homogeneous population of weakly zoned phenocrysts. By contrast, plagioclase from the intermediate to silicic volcanic lithic fragments in the Rockland...