630 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



Fig. 39.16. Potassium-argon dates in British Columbia Mackenzie District and Yukon Territory. 

 Map kindly supplied by R. E. Folinsbee. See Baadsgaard, Folinsbee and Upson, 1961 



Alaska, and down the Yukon River, possibly to the junction with the 

 Tanana River. The bedrock is so much covered by alluvium from the 

 Tanana down the Yukon Valley that the further course of the fault zone, 

 if existent, is not evident. 



Farewell-Shakwak Fault Zone 



The most arresting alignment of valleys and mountain fronts starts on 

 the northwest front of the Alaska Range (Mt. McKinley) and extends 

 eastward as a trench through the southern part of the Alaska Range from 

 Cantwell to Miller's Roadhouse, thence southeastward along the north- 

 east front of the Mentasta and Nutzotin Mountains. It then crosses the 

 border, follows along the Alaska Highway to Kluane Lake and to 

 Dezadeash Lake where it jogs a bit to extend to the "Haines Cut-off" 

 valley. It follows to the Lynn Canal. A branch may go out Chatham 

 Straight, but the main fault appears to follow along Stephens Passage to 

 Wrangell. The great fault zone has been named the Farewell in the 

 Kuskokwim region and the Shakwak in the Yukon. 



Mt. Logan Fault Zone 



Not specifically pointed out in the literature as far as the writer knows 

 is a major narrow topographic lineament just south of the Farewell- 

 Shakwak zone. It is labeled "Mt. Logan Fault Zone" on the map of Fig. 

 39.2. Reginning on the southeast at Chatham Strait it proceeds as a 

 trench along Icy Straight and Glacier Ray through the Mt. St. Elias Range 

 to and along the Hubbard Glacier Valley. It then extends along the 

 Logan Glacier Valley and the Chitina River. It thence passes a little south 

 of the town of Chitina and down the Matanuska River Valley to 

 Matanuska. It continues southeastward along the base of the mountains 

 east of Anchorage to Kachemak Ray. This postulated fault zone is not as 

 smoothly curved or linear as the others. 



Chugach-St. Elias and Fairweather Faults 



A great fault has been described in the Tertiary province of southern 

 and southeastern Alaska and it is illustrated in Fig. 39.9. It is also vividly 

 expressed on the relief maps. 



