UPLIFTS AND BASINS IN THE ROCKY MOUNTAINS. 255 



range or Grand Encampment mountains. It disappears beneath the pres- 

 ent east and west depression of central Wyoming ; but a submerged line of 

 uplift, proving a possible connection with that of the Wind River mountains, 

 is found in the Archaean exposures of Rawlins peak and the Sweetwater 

 mountains. 



Immediately west of the Colorado mountain mass are the broad valley 

 depressions of North, Middle, and South parks. 



Southwest of Pike's peak and separating the Colorado range from the Wet 

 mountains is a bay-like depression extending northwestward from Canon 

 City toward the southern end of the South park. 



The Wet mountains form the mountain front from Canon City south to 

 Huerfano park, and have a small depression or park to the westward, known 

 as the Wet Mountain valley, which is of less orographical significance than 

 those already mentioned, having once probably been part of an elevated 

 region, brought down to its present position by faulting and erosion in more 

 recent times. The northwestern continuation of the Wet mountains has 

 also lost its former topographical importance, but is recognized geologically 

 in the Arcrnean area along the Arkansas river, west of the Royal gorge. 



Huerfano park is a second bay-like depression, which, if extended to the 

 northwest, would merge into the Wet Mountain valley. It separates the Wet 

 mouutains from the Saugre de Cristo range, which, rising gradually from 

 the plains of New Mexico, forms the east front of the Rocky Mountains as 

 far north as Huerfano park, and then trends northwestward, forming the 

 western boundary of that park and of the Wet Mountain valley in the same 

 general line of uplift as the Sawatch range. 



The original Sawatch uplift, now divided by the upper Arkansas valley 

 into the Sawatch and Mosquito ranges, formed the earlier western boundary 

 of the South park depression, as the Mosquito range does to-day. 



The western boundary of the Middle and North parks is formed by the 

 Park range, a line of uplift also having a northwesterly trend parallel to 

 that of the Sawatch and set off en echelon a little to the northeast of it. Its 

 northwestern end is known as the Grand Encampment mountains, and the 

 southern continuation, which at times has been separated from it, is called 

 the Gore mountains. 



To the southwest and west of the Sangre de Cristo is the great valley 

 depression of the San Luis park, on the same general meridian with the 

 other parks, but geologically distinct in that it is probably of more recent 

 formation, since there is no evidence that Mesozoic sediments were ever 

 deposited in it. To the northwest, and separating it from the head of the 

 Gunnison and lower Grand rivers, is a broad area of moderate elevation 

 now buried beneath extensive bodies of igneous rocks. But little can now 

 be learned by actual observation of the structure of the underlying rocks of 



XXXIV— Bull. Gf.ol. Soc. Am.. Vol. 1, 1889. 



