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GUIDEBOOK OF THE WESTERN UNITED STATES. 



spanning gulches, and finally scaling the south wall of the canyon. 

 The line takes a short cut for the valley of Roaring Fork, up which 

 it is carried to and across the Continental Divide at Hagerman Pass. 



So far the geologic structure of the great upfold (anticline) is 

 comparatively simple, having been broken at one point only. The 

 highest point in the fold, the axis, is passed near milepost 354, and 

 beyond that point the quartzite rapidly approaches railroad level, 

 but it is broken by so many faults that few travelers can trace the 

 fomiations and understand the manner in which they appear and 

 disappear. By the aid of the map, however, those who are interested 

 in geologic structure may obtain a fairly good idea of what has 

 happened here and of the shape in which the rocks were left. 



All the formations are regular as far as milepost 355, near Grizzly 

 siding, where the quartzite has been abruptly dropped from a height 

 of at least 350 feet above the railroad to water level. This change 

 in the position of the rocks is the result of a fault,*^ which trends 

 slightly west of north, probably cutting the high bluff on the west 

 side of Grizzly Creek, which here enters the river from the north. 

 Be3'ond this fault the beds rise gradually until the white quartzite, 

 which is at water level at Grizzly, is above the railroad and the 

 canyon is rough and rugged, as shown in Plate LIX. Half a 

 mile beyond milepost 356 about 50 feet of the pink quartzite has 

 made its appearance. At this point the granite on the opposite side 

 of the river rises to a height of at least 300 feet. This discrepancy 

 marks another fault, which does not cross the railroad but trends 

 nearly east and west directly along the stream. The rocks on the 

 south side of this fault have dropped about 300 feet, or those on the 

 north have been lifted a similar distance. 



Beyond the point where the railroad approaches the fault most 

 closely the rocks descend, and within a short distance most of the 

 quartzite has disappeared; but the road here enters Xoname Park, 

 and it is almost impossible from the moving train to determine the 

 structure. However, a little farther along the Leadville lime- 

 stone also dips steeply toward the south and is broken by a fault 

 that runs nearly parallel with the one just described. This fault 

 lies near the south wall of the park. The Leadville limestone is 

 dropped on the north side of the fault and may be seen topping the 



^ As the term " fault " means a 

 break in the rocky strata of the earth 

 and as the breaking is always accom- 

 panied by slipping and crashing, one 

 might expect to find tlie surface of the 

 gi'ound disturbed along a fault. It 

 undoubtedly is disturbed when the 

 movement takes place, but all the 



faults seen from the Denver & Rio 

 Grande Western trains occurred so 

 long ago that any break or disturb- 

 ance of the surface they caused has 

 been obliterated by the streams and 

 the weather. Examples of the lack of 

 evidence of faults on the surface are 

 shown in Plate LXXXVII, A and B. 



