Holocene tephra stratigraphy in four lakes in southeastern Oregon and northwestern Nevada, USA

To better understand the regional tephra stratigraphy and chronology of northern Nevada and southern Oregon, tephras in archived cores, taken as part of the Steens Mountain Prehistory Project from four lakes, Diamond Pond, Fish and Wildhorse lakes in southeastern Oregon and Blue Lake in northwestern Nevada, were reexamined using more advanced electron microprobe analytical technology. The best preserved and most complete core from Fish Lake along with Wildhorse Lake hosted two tephras from Mt. Mazama (Llao Rock and the Climactic Mazama), a mid-Holocene basaltic tephra from Diamond Craters, Oregon, two Medicine Lake tephras and an unexpected late Holocene Chaos Crags (Mt. Lassen volcanic center) tephra which was also found in the other lakes. Blue Lake was the only lake that hosted a Devils Hill tephra from the Three Sisters volcano in west central Oregon. Another tephra from the Three Sisters Volcano previously reported in sediments of Twin Lakes in NE Oregon, has now been confirmed as Rock Mesa tephra. The Chaos Crags, Devils Hill and Rock Mesa tephras are important late Holocene stratigraphic markers for central and eastern Oregon and northwestern Nevada.