338 / HARLEN BRETZ 



through it are numerous Hght-colored granitic pebbles and cobbles, 

 which were brought by the Juan de Fuca Glacier over the divide 

 between the Straits and Soleduck River. The Soleduck Valley 

 train was built after the front of the ice had withdrawn eastward to 

 a position somewhere near Lake Crescent. Indeed, aggradation 

 from Olympic debris alone may have continued long after the Juan 

 de Fuca Glacier had retreated entirely from the Soleduck drainage. 



The thickness of the Juan de Fuca Glacier was sufficient to 

 enable it to cross the divide between the Straits and the Soleduck 

 valleys. The British Admiralty chart shows summits in this range 

 4,000 feet high, but the crest in general can hardly average 2,000 

 feet. Enough of the range was overridden to allow a continuous 

 glacier to spread out on the coastal plain to the south, as shown in 

 preceding paragraphs. Better figures on the thickness of the 

 glacier are to be obtained from features of the Elwha Valley, a few 

 miles east of Crescent Lake. 



No granite is known in situ in the Olympic Mountains. 

 "Float granite" however occurs in the lower portions of several 

 Olympic valleys draining to Puget Sound and Fuca Strait, 

 and very probably has been derived from Cordilleran ice which 

 pushed up on the flanks and back into the valleys of both the 

 eastern and northern sides of the Olympics. 



The river gravel of the Elwha Valley contains scattered granitic 

 bowlders and cobbles at least as far up as Elkhorn Ranger Station, 

 15 to 20 miles by valley from the Strait. Granitic erratics are 

 abundant along the trail some hundreds of feet above the valley 

 bottom at least 1 5 miles south of the Strait. 



No lobe of ice from the northern glacier could have pushed this 

 far up the narrow Elwha Valley from the lowland occupied by the 

 Juan de Fuca Glacier, and if these bowlders record the presence of 

 ice originally from Georgia Strait, the thickness of the Juan de 

 Fuca Glacier must have exceeded the height of the ridges it had to 

 cross. Hurricane Hills, the highest ridge directly i-n the path of 

 such invading northern ice, attains an altitude throughout its 

 length of 5,000 feet. Juan de Fuca Strait to the north is 600 feet 

 deep. The Juan de Fuca Glacier opposite the mouth of the Elwha 

 Valley therefore must have been more than a mile thick. This is 



