MAE\"IXE.J 



GEOLOGY— FRAZIER BASIN. IGl 



ing Mil /t, and south of the morainal mass g, is occupied by loose gravel 

 deposits covered with a fine dusty soil, which occur in a flat terrace, ris- 

 ing about 50 or 60 feet above the main stream. Near the center of this 

 area is a low ridge which much more resembles the lake deposits farther 

 down the Grand. No exposure showing the actual relations between 

 this ridge and the lower terraces was observed, but the general im- 

 pression received was that the former was the older — a hill of erosion, 

 surrounded by the more recent terraces. If so, the latter were probably 

 deposited beneath the waters of the lake formed by the dam of lava, and 

 filled up the previously eroded valley surface. 



The Grand, after leaving the small caiion through the granite mass 

 Z, flows out into a flat terraced basin, where it is joined by Willow Creek 

 and the Frazier Eiver, and which forms a portion of the most interest- 

 ing geological region of the park, before describing which, however, we 

 will turn to the drainage basin of the Frazier. 



THE FRAZIER BASITs\ 



South of the East Fork of the Grand the westward mountain-slopes, 

 as has been previously mentioned, are far more smoothly contoured and 

 gently molded than north of that stream. These massive slopes fall to 

 the area about the junction of the Frazier and Grand, and form a low 

 northern side to the upper Frazier basin. Southward, the lateral ex- 

 tension of the same slopes, which retain their former characters, descend 

 from the main divide and form the east side of the basin. Sweeping 

 around westward they fall from the Berthoud Pass ridges northward to 

 its southern border. The western border of the basin is more ridge- 

 like, with accompanying hills ; is much lower than the east and south 

 sides, but retaining a rather even top. 



The James Peak group stand at the southeastern corner of the basin, 

 Mount Bj'ers at its southwestern corner. The natural outlet of this 

 basin is at the northwest corner, where the surrounding granite ridge 

 rises scarcely 300 feet above the river in a broad gentle divide, passing 

 over into the basin of the Grand, and across which the Berthoud, James 

 Peak, and South Boulder trails, after uniting, pass to the Hot Springs. 



The Frazier, however, has cut its outlet by a rugged and imijassable 

 canon — about six miles long and several hundred feet deep — through 

 the spur of metamorphic rocks a few miles east of this divide. All of 

 these surrounding mountain-slopes are of the metamorphic crystalline 

 archsean rocks. Their contours seem to indicate a surface of former 

 subaqueous denudation, covered subsequently with sedimentary rocks, 

 which have not so very recently been entirely eroded away, leaving 

 their impress still on the underlying rock surfaces. Indeed, some ap- 

 pearances upon the western side of the basin would seem to indicate 

 that patches of such sedimentary rocks may still remain, though they 

 were not visited.* 



Glacial action alone could never have effected such wide-spread uni- 

 formity of character. 



All the flat lower central portions of this basin, forming an area ap- 

 proximately five miles in diameter, are occupied by sedimentary rocks 

 which have been eroded into distinct though low terraces. The dis- 

 tribution of trees is here quite marked, being confined to the granite 

 slopes, and apparently to above a certain level on the higher terraces, 



* Major Powell informs me that he found some small areas of siliceous saudstones, 

 probably Cretaceous No. 1, thus resting on both sides of the western lidge of the Fra- 

 zier basin. 



11 G S 



