90 GEOLOGICAL SURVEY OF THE TEREITORIES. 



PRINCIPAL TOPOGRAPHICAL FEATURES OF THE MIDDLE PARK. 



We have already seen how tlie branches of the Grand join it from the 

 northeast and south, like the rays of a great irregular leaf uniting with 

 the parent stem. Along the main Grand, especially where joined by its 

 tributaries, and following along some of the latter, are flat, open and 

 treeless areas, which may be considered as forming the Middle Park 

 proper. The ridges separating these tributaries are mostly well defined, 

 some reaching altitudes of from 2,000 to 4,000 feet above the adjoining 

 streams. These are mostly of sedimentary rocks, and quite different in 

 character from the mountains of harder metamorphic rocks forming the 

 main range. 



The Middle Park thus differs from both the Korth and South Parks 

 on either hand, which are much better defined, large, basin-like areas 

 less broken up by local ranges. Indeed, the Middle Park is a sort of 

 accidental middle ground between the two. The more important geo- 

 logical dividing line between the North and South Parks is the great 

 fold which causes the massive spur of metamorphic rock west of the 

 Gray Peak mass, joining it with the Park range, though cut through by 

 the Blue. Between the Middle and North Park no such profound zoo- 

 logical fact exists ; there is no folding whatever, but the divide has been 

 determined by the masses of hard eruptive rocks which have here found 

 vent and protected the softer rocks below from erosion. Indeed, it is 

 just possible that the drainage of the Middle Park once had its outlet 

 into the North Park. 



In speaking of the more special topographical features of the Middle 

 Park region, those portions adjacent to the high eastern ridge have 

 already been referi-ed to. Such is the rugged, caQon-cut mountain 

 area west of Long's Peak, separated by the East Fork of the Grand from 

 the more gently-contoured massive spurs to the south, which swing 

 around with the main ridge from Arapahoe, through the James Peak 

 group to Mount Byers, inclosing on the east, south, and west sides, and 

 partially on the north, the basin-like drainage-area of the Frazier. The 

 latter river, after collecting the surrounding waters, escapes from this 

 basin by a caiion carved through about six miles of the low northern por- 

 tion of the surrounding granite, and enters the basin of the Grand. . The 

 main fork of the Grand, before joined by the east fork, occupies a re- 

 markably well-defined, trough-like valley, trending directly north and 

 south. Its headwaters rise in the deep gorges separating the main 

 range from the high southern end of the Medicine Bow Mountains, 

 whose northern extension forms such a symmetrical eastern border to 

 the North Park. But where it crosses the north line of the district the 

 V form has changed to the U form, with a comparatively flat bottom, 

 between one or two miles broad, while the ends of the massive spurs 

 forming its sides rise abruptly, but in rather smooth curves, on either 

 hand. 



The eastern slope of the valley retains its height and character all 

 the way down to where joined by the East Fork, though cut by the many 

 gorges draining the mountain area. The western slox^e, at the north, rises 

 equally high and steep, though the crest being less distant it is cut by 

 lesser canons. Toward the south the top of the ridge becomes smoother 

 in contour and gradually falls, finally giving way to the flatfish region 

 adjacent to the Grand. Here the latter turns westward and in a basin- 

 like terraced area receives the waters of Willow Creek from the north 

 and of the Frazier from the south. Passing on west it flows through 



