Pre-late Wisconsin valley-glacier erratics between Leavenworth and Peshastin, Wenatchee valley, Washington

Abstract

The late Wisconsin Icicle Creek alpine glacier transported tonalite boulders from the Mount Stuart batholith to arcuate end moraines in Icicle valley and Wenatchee valley near Leavenworth. Some previous workers considered sparsely weathered Mount Stuart boulders lying outside these moraines and draped by silt as having been ice rafted in a late Wisconsin lake. But the boulders are more likely within drift or end moraines of pre-late Wisconsin glaciations correlative to lateral moraines on Boundary Butte. The silt—a younger deposit that covers the boulders—derives not from a physically ponded lake but apparently from brief Missoula flood(s) backflooding up the valley.