202 



ANNOTATED GUIDE. 



(Golden to Savona.) 



BY 



Reginald A. Daly. 



Miles and 

 Kilometres. 



35-3 m. Golden — Alt. 2,578 ft. (786 m.). The train 

 56-8 km. here enters a typical section of the Rocky 

 Mountain trench, a through-going Cordilleran 

 feature of a length hardly to be matched in 

 any other mountain chain. About 100 miles 

 (160 km.) above Golden is the source of the 

 Columbia river, which, except for a short 

 distance, occupies the main trench as far as 

 the beginning of its "Big Bend", 87 miles 

 (140 km.) below Golden. 



The town overlies Ordovician shales; the 

 long bastion-like escarpment of the Dogtooth 

 range (Purcell Mountain system) across the 

 valley is composed of the uppermost slates, 

 schists, and quartzites of the Beltian series. 

 The trench is, in fact, here located on a master 

 longitudinal fault of a throw at least equivalent 

 to the entire thickness of the Cambrian group 

 (5700 m.). The fault plane runs close to 

 the lower cliffs of the Dogtooth mountains. 

 It has clearly located the trench, which, how- 

 ever, has been specially widened by erosion 

 on the softer Paleozoic rocks ranging east of 

 the great break. The fault probably dates 

 from the Laramide (post-Laramie and pre- 

 Eocene) revolution. The colossal denudation 

 represented in the destruction of the uplifted 

 Purcell block must have consumed much of 

 Tertiary time. What part of the period was 

 concerned with the excavation of the visible 

 trough it is still impossible to say. The work 

 was done in stages. In the later Tertiary the 

 trench has been increased to widths of three to 

 six miles (5 to 10 km.), a past-mature river 



