Roadcut on Burpee Hill Road reveals glacial till overlying advance outwash (stream deposits) from Cordilleran glacier.
|
Burpee Hill
The Puget Lobe outwash
Travelers bound for Baker Lake by way of the Burpee Hill Road have opportunity to view thick deposits of well-bedded sand and gravel deposited about 17,000 years ago (Pleistocene), when a tongue of the Cordilleran ice sheet advanced up the Skagit Valley, and sediment-loaded rivers emerging from the glacier snout deposited sand and gravel in front of the glacier. The road winds in and out of alcoves in these unstable deposits, each alcove the bite of a landslide. A layer of moraine, that is unsorted rock debris and glacial sand and silt (the stuff of ice-borne till) tops the well bedded sands and gravels, and can be seen sometimes in the cut bank at the top of the grade. The outwash, deposited as the glacier advanced, and the till cap show that the outwash was overridden by the advancing ice. Because the road cuts continually slump and change, the till cap may be hard to find.
|
