THE JUAN DE FUCA LOBE OF THE CORDILLERAN 



ICE SHEET 



J HARLEN BRETZ 



There were two large glaciers in western Washington during the 

 latest, or Vashon, glaciation of that region. Each was essentially 

 an elongated lobe of the great piedmont glacier which accumulated 

 between the mountains of Vancouver Island and the British Co- 

 lumbia mainland. One lobe moved southward into the Puget 

 Sound depression, filling it completely and pushing over into the 

 Chehalis Valley to the south. The other moved westward through 

 the Juan de Fuca Valley, extending as a tidewater glacier into the 

 open waters of the Pacific Ocean. Though both of these lobes were 

 augmented to some extent by valley glaciers from mountains in 

 Washington, neither were true piedmont glaciers of these moun- 

 tains. 



Ice from this piedmont glacier in the depression now occupied 

 by Georgia Strait moved almost directly south over the San Juan 

 Islands, striating and grooving rock surfaces from tide-level virtually 

 to the summit of the highest peak of the islands, 2,400 feet A.T. 



In Fuca Strait south of the islands, the ice divided into two 

 parts, one continuing southward as the Puget Sound Glacier, the 

 other being deflected to the west and north of west as the Juan de 

 Fuca Glacier. The Puget Sound Glacier pushed as far south as 

 latitude 46° 50' N., about 80 miles south of the re-entrant angle 

 between the two lobes. Its extra-morainic outwash extended down 

 the Chehalis Valley to the head of Grays Harbor, 30 miles beyond 

 the limits of the ice.^ 



The Juan de Fuca Glacier extended westward along the south- 

 ern coast of Vancouver Island nearly to Cape Beale^ and spread 



'J H. Bretz, "Glaciation of the Puget Sound Region," Washington Geological 

 Survey, Bulletin 8 (1913). 



^ C. H. Clapp, "Southern Vancouver Island." Canada Geological Survey, Memoir 

 13 (1912), p. 144. 



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