[schofield] rocky MOUNTAIN TRENCH 95 



present streams such as the Fraser, Kickinghorse, and Elk Rivers 

 were formed. These rivers flow westwards into the trench with very- 

 steep gradients in contrast to the gradients of the Athabaska, Bow, 

 and the Oldman Rivers which flow eastwards in the old "through 

 valleys" as small remnants of the large rivers which occupied these 

 valleys in Eocene times before the faulting occurred along the Rocky 

 Mountain trench. These events caused the continental divide to 

 shift its position from west of the Rocky Mountains to its present 

 position east of the trench and gave rise to the formation of the 

 Yellowhead, Kickinghorse, and Crowsnest "passes." 



The faulting did not extend to any distance north of the "Big 

 Bend" of the Fraser. McConnell ^ in his examination of the Finlay 

 River section did not find any evidence of faulting. This explains 

 the fact that the Peace River crosses the Rocky Mountain trench 

 without interruption. Thus the Rocky Mountain trench may be 

 divided into two portions, a northern one which includes the Peace 

 River drainage due to normal river erosion, and a southern portion 

 which is due to faulting, primarily. 



The Post-Eocene History (Figure 5) 



In Eocene times the south-flowing Columbia River, a Cretaceous 

 river rejuvenated by the uplift at the close of the Cretaceous, occupied 

 a valley about 100 miles west of the Rocky Mountain trench and had 

 no connection with the drainage of the trench. The course of this 

 river, since it is almost north and south, if projected headwards would 

 intersect the Rocky Mountain trench whose trend is northwest- 

 southeast. The elevation of this Columbia valley at the close of the 

 Eocene was probably between 1,000 to 1,500 feet below the level of 

 the floor of the Rocky Mountain trench since the present elevation 

 of the floor of the Columbia valley is about 1,000 feet above sea-level. 

 During post-Eocene times, in the Miocene or Pliocene, the headward 

 erosion of the south-flowing Columbia River eventually intersected 

 the Rocky Mountain trench and diverted part of the waters of the 

 Rocky Mountain trench into the Columbia River. Thus the "Big 

 Bend" of the Columbia was formed. Subsequent headward erosion 

 southwards along the trench produced the rapids and falls which 

 occur as far south as Donald and the cafion in the Beaver River on the 

 west side of the trench as it approaches the Rocky Mountain trench. 



The history of the Fraser River and the origin of the "Big Bend" 

 of the Fraser is difficult to decipher since the information concerning 



> McConnell, R. G., Geol. Surv., Can., Ann. Rept., 1894, vol. VII. 



