GLACIAL LAKES OF PUGET SOUND 

 PRELIMINARY PAPER 



J. HARLEN BRETZ 



On the western margin of the North American continent an 

 uninterrupted fjord coast extends from Cross Sound in the Alaskan 

 panhandle southward to Puget Sound in the state of Washington. 

 The topographic expression of the whole extent of coast line is 

 glacial/ but the Strait of Juan de Fuca appears to separate this coast 

 into (i) a region of predominant glacial erosion and (2) a region 

 where glacial deposition much exceeded the erosion of the ice. Puget 

 Sound is this latter region to a unit. 



The complexly fingered arm of the sea known as Puget Sound 

 lies in meridionally oriented troughs whose walls sometimes rise in 

 sea cliffs 300 feet A.T. and whose maximum depths are approxi- 

 mately 1,000 feet below sea-level. To sea -level, at least, these fjord- 

 like troughs are largely drift-walled. The larger stream valleys, lake 

 valleys, and divides of the Puget Sound region are likewise fashioned 

 in glacially transported material, and all share the roughly meridional 

 orientation. 



It is established that the ice of the last glaciation of Puget Sound 

 was derived largely from snowfields to the north.'' The axial lines 

 of the grooved topography parallel the striae, and the ridges and 

 valleys are at least veneered and often deeply covered by the youngest 

 till of the region. The Vashon-^ ice which deposited that till sheet 

 must have been related to the genesis of this peculiar and persistent 

 topography in one of three ways: (i) the ice conformed closely to 

 the ridges and grooves which were fashioned before its advent; 

 (2) the last glaciation produced the present topography by erosion 

 of an older and more nearly uniform drift surface; or (3) the Vashon 



1 G. K. Gilbert, "Glaciers and Glaciation," Harriman Alaska Expedition. 



2 Bailey Willis and G. O. Smith, "Tacoma Folio, No. 54," ^7.5. Geological Survey. 



3 Willis names the last glaciation of Puget Sound from Vashon Island, where its 

 till is typically developed ("Tacoma Folio," U.S. Geological Survey). 



