PHYSIOGRAPHIC DEVELOPMENT IN COLORADO 



129 



Cedar Creek, which enters the Thompson Valley about a mile 

 west of Mont Rose, is also open and U-shaped, with steepened sides 

 in accordance with the main valley. Small tributaries of the 

 Thompson within the fourth unit are narrow gulches developed by 

 recent stream erosion. All the gulches from Estes Valley to Mont 

 Rose, however, were begun before the last cycle of canyon-cutting. 

 When traced from their junction with the Thompson to their head- 

 waters they show a narrow steep- 

 walled canyon in the lower 

 reaches opening out into wider 

 middle and upper portions. 



5. The fifth unit is the Love- 

 land Canyon (Fig. 3). From 

 Mont Rose to the foothills the 

 valley is a deep box canyon 

 whose sides rise from 100 to 

 1,000 feet above the stream. 

 The lower walls are nearly verti- 

 cal and are the dipping surfaces 

 of almost perpendicular beds of 

 highly indurated schist. For 

 the most part the river's course 

 lies along the strike of the 

 schistosity and crosses the dip 

 only at right angles with sharp 

 and short turns. 



The second and fourth units 

 have the following features in 

 common: (i) open flat-bottomed valleys with steep walls; (2) 

 intrenched meanders in the bottom of the broad valleys. The 

 third and fifth units also have many similar features as: (i) narrow, 

 V-shaped outlines; (2) precipitous tributary gulches (Fig. i). It 

 will be shown that the second and fourth physiographic units have 

 had a similar development, but entirely different in its aspects from 

 the processes which developed units 3 and 5. 



The course of the Big Thompson River lies almost at right 

 angles to the strike of the Front Range and reveals a section of 

 the Pre-Cambrian beds from the Continental Divide to the foothills. 



Fig. 3. — Same location as Figure 2 

 but looking downstream into the gorge of 

 unit 5. 



