88 GEOLOGICAL SURVEY OF THE TEERITOKIES. 



sent the same smooth and rounded contours as those on the east side of 

 the Frazer basin. From the northeast corner of the loop a high spur 

 runs out, separating the Williams and Frazer drainage, and culminat- 

 ing in Mount Byers, (12,778 feet,) one of the most commanding points 

 of all the Park region, at the north. 



The western side of the loop is a rugged mountain ridge, with, I be- 

 lieve, a difacuit pass, called Jones's Trail, across to the headwaters of 

 Williams Kiver. The descent to the main valley of tlie latter, along 

 the west side of this loop, and from the Mount Byers ridge, is in. great 

 massive spurs, descending rather abruptly, but still quite evenly, and 

 cut by deep gorges. The Gray's Peak ridge is much the same, rugged 

 and grand, yet, on the western side, with an obvious tendency in the 

 spurs to a g-eneral plateau-like area, though it is almost obliterated by 

 the many caiions. Directly beside the peak, passing almost over its top, 

 is a fair'trail for animals to pass, while a few miles to the east a wagon- 

 road is built, crossing the range at the Argentine Pass at an altitude 

 of about 13,200 feet, and connecting Georgetown with Montezuma and 

 the other mining towns upon the headwaters of the Blue Eiver. Nearer 

 Mount Evans a trail crosses the Evans spur from Georgetown over 

 into the South Park. 



Eastward from Evans the spur is continued by a long ridge-like 

 line of hills, reaching nearly to the plains, and separating the waters 

 which flow southward into the South Platte, and without my district, 

 from those which flow eastward and into it. It forms, with the course 

 of the main divide upon the west, a natural southern boundary of the 

 district. 



PRINCIPAL TOPOGKAPHICAL FEATURES OF THE EASTERN SLOPE. 



The crest of the main divide as thus traced may be considered as pre- 

 senting, as a whole, a flat convexity to the east, on which side its prin- 

 cipal characteristic is abrupt slopes, usually in high precipices, sur- 

 rounding profound amphitheaters. Extending eastward from these 

 first abrupt slopes is a zone of mountain country which is narrowest at 

 about the center of the district, where it extends about seventeen miles 

 east from the main crest, but widening at the north and south borders 

 of the district to nearly thirty miles. The eastern face of this zone 

 thus presents a flat concavity to the east, the general trend of which is 

 north and south, while the depression westward in the center is about 

 ten miles. 



This eastward border of the mountain-zone is exceedingly sharp and 

 well defined, and all along it the mountain-spurs abruptly give way to 

 the plains which stretch away uninterruptedly far to the east. 



This mountain-zone can in nowise be regarded as made up of dis- 

 tinct ranges or a system of ridges, but as a unit in itself, having charac- 

 teristics which hold very uniformly over nearly all its parts. From be- 

 neath the precipitous crest, from all the gorges and amphitheaters at its 

 base, flow innumerable streams which, after emerging from these upper 

 caiions into the smoother highlands, soon collect into a few principal 

 watercourses, generally uniting where they are not in deep canons. 

 Flowing in a generally eastern course these gradually sink their chan- 

 nels deeper and deeper into the rocks, the different main streams uniting 

 their canons here and there, and finally issue from their deep-cut gorges 

 in the mountain-front to flow out into the i:)lains and" to the Platte. 

 Though over fourteen main branches may be considered as rising 

 within the fastnesses of the main crest, their united waters break through 



