[schofield] rocky MOUNTAIN TRENCH 63 



The Geography of the Rocky Mountain Trench 



The most remarkable topographic feature of the Canadian 

 Cordillera is the Rocky Mountain trench, so designated by Daly,^ who 

 uses as an analogy a military trench traversing a hilly country. Much 

 information concerning this depression had been gained during that 

 period from 1871-1900 which in the researches of British Columbian 

 geology may be called the exploratory period. It was made note- 

 worthy by the researches of Selwyn, Dawson, and McConnell, who 

 laid the foundations on which all the later workers in the Cordillera 

 have built their superstructures. In the eastern portion of the 

 Cordillera where the Rocky Mountain trench is situated, later detailed 

 investigations have been carried on principally by Daly', but to some 

 extent by McEvoy and Malloch. 



The Rocky Mountain trench forms the western boundary of the 

 Rocky Mountains practically throughout its whole length, a distance 

 of over 800 miles, extending from south of the International Boundary 

 line at the 49th parallel of latitude almost to the Yukon-Alaska 

 boundary in latitude 61 degrees. The location of the trench after it 

 crosses the boundary between British Columbia and the Yukon, 

 is not known with any degree of certainty. The trend of this topo- 

 graphic feature, which ranks among the great structural valleys of the 

 globe, is almost constant in a direction north 33 degrees west. This 

 trench is occupied by the following rivers and streams: Flathead 

 (north-fîowing), Kootenay (south-flowing), Columbia (north-flowing), 

 Canoe (south-flowing). Fraser (north-flowing), Parsnip (north-flowing), 

 Finlay (south-flowing), Kachika (north-flowing), and the Hyland. 



From this point the trench cannot be traced with any degree of 

 certainty, but it may follow the valleys occupied by the Pelly and 

 Yukon, which trend more closely to the northwest. 



One of the most peculiar features of the trench, whose walls on 

 both sides rise on an average 4,500 feet above the valley floor, is the 

 fact that it is occupied by streams which vary greatly in size. For 

 example, the Kootenay River enters the trench as a large river from 

 the north, while less than a mile away from this point, the north - 

 flowing Columbia has its beginning in two small lakes. In the same 

 manner, the south-flowing Canoe River rises and continues as a very 

 small river to join the mighty Columbia in the trench. From these 

 examples, which might be greatly amplified, it can be seen that the 

 size and depth of the valleys which unite linearly to form the Rocky 

 Mountain trench bear no relationship to the size of the streams which 



1 Daly, R. A., Geol. Surv., Can., Mem. 38, 1912, p. 26. 



