NOTES ON THE SURFACE FEATURES OF THE COLORAL'O OR 

 FRONT RANGE OF THE ROCKY MOUNTAINS. 



Bv F. V. Hayden. 



The geological structure of the eastern base of the Rocky Mountains, 

 from Cheyenne to Pueblo in Colorado, has been so carefully studied 

 that but little more can be said that will have the air of novelty. It 

 remains now to present to the eye a more connected view of the topo- 

 graphical features of this region, thus rendering much clearer many 

 points in the geology. The beautiful and accurate illustrations of Mr. 

 Holmes which accompany these notes will convey a clearer conception 

 to the minds of geologists, of the topographical forms, as well as the 

 geological features, of this interesting portion of Colorado, than pages 

 <j»f mere description. With these views before the reader the detailed 

 investigations of Mr. Marvine, Dr. Peale, and Dr. Endlich, as well as 

 those of the writer, in the annual reports for 1873 and 1869, will be 

 far better understood. Therefore, it will not be necessary to repeat in 

 this connection the details of the geology of this region, but the reader 

 is referred to the series of annual reports. Plate IX represents the great 

 Colorado or Front range of mountains, as seen from a point near Denver, 

 commencing north just beyond the northern boundary of Colorado and 

 extending south to Pike's Peak, a distance of about eighty miles in a 

 straight line. In the foreground we see what are termed the plains, a 

 broad rolling surface, gradually sloping from the base of the mountains 

 eastward. The dotted line marks the boundary between the sediment- 

 ary strata and the Archsean or Metamorphic rocks which form the 

 nucleus of the range. At different points the uplifted ridges, which are 

 termed in the West " Hogbacks," can be distinctly seen. This view was 

 taken twenty miles or more to the eastward of the immediate base of 

 the mountains, and therefore only the higher ridges were visible to 

 the eye of the artist, but their character can be well understood 

 from these sketches. North of the North Boulder Creek, at I, I, the 

 ridges of red sandstone with Cretaceous No. 1 are well exposed near the 

 base of the range, but are not shown in the sketch ; between the North 

 and South Boulder Creeks at i^, I, and h, are some of the most conspicuous 

 ridges of sandstone that are known to occur along the foot of the Rocky 

 Mountains, from latitude 49° south to Santa h'e. They rise to a height 

 of 1,500 feet above the plains at their base. It is difficult to account 

 for the manner in which they have been protected from erosion. It is 

 quite possible, however, that it is due to the fact that they have been 

 partially metamorphosed by heat, and hence their greater hardness 

 renders them less amenable to the influence of the atmospheric forces. 

 That these ridges, all along the base of the mountains, were originally 

 much higher and may have even extended far up the mountain-sides, 

 but have been removed by erosion, there is ample evidence. In many 

 instances they seem to have been almost entirely removed for con- 

 siderable distances, and again they rise 200 to 500 feet, seldom more, 

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