Zircon grains separated from altered ash beds were analyzed to better understand the ages of beds. Isotopic analyses for U-Pb geochronology and trace element geochemistry were performed simultaneously by secondary ion mass spectrometry using the Stanford-USGS SHRIMP-RG ion microprobe housed at Stanford University, USA. Analyses followed the analytical protocol and data acquisition conditions described by Watts et al. (2016). These data are reported in this Release.