Rhyolite Roadcut, Mt. Washburn

A road cut near Dunraven Pass, exposing a rhyolite conglomerate, provides an excellent opportunity for a small exercise in relative dating. The clasts of the clast-supported conglomerate show little rounding. A basaltic dike cuts through the conglomerate, proving that it is younger than the conglomerate. Finally, movement on a small fault offset both the conglomerate and the dike, making this event more recent than the deposition or the conglomerate and intrusion of the basaltic dike.






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