The presence of the Glacier Peak G ash and the underlying St. Helens Jy ash in laminated lake sediments near Marias Pass indicates that in this region the Continental Divide was ice free before about 11 400 BP. Macrofossils, pollen, and spores in these same sediments indicate establishment of shrubs, herbs, and scattered conifers by that time. At Sun River Canyon, about 90 km south of Marias Pass, presence of the Glacier Peak G ash in a postglacial alluvial fan indicates that glacial ice had receded upvalley from the canyon mouth and that the Sun River Glacier no longer existed by 11 200 BP. -from Authors
Additional Publication Details
Deglaciation of the mountainous region of northwestern Montana, U.S.A., as indicated by late Pleistocene ashes.