Instrumental neutron activation analysis (INAA) was used to correlate volcanic ash layers in several peat bogs in eastern Oregon. The concentration of 19 elements in glass separates from most of the ash layers indicates correlation with Mazama pumice sampled near Crater Lake, Oregon. Radiocarbon dates of the peat also verify the ash as Mazama. The ash is 18 cm thick at a distance of 450 km from the source. Two other ash layers, one ∼2,775 yr B.P. and one >9,640 yr B.P., occur in bogs of northeastern Oregon.