ENDLicH.] GEOLOGY SAN LUIS DIvSTEICT, SECTION B.* 323 



CHAPTEE III. 



GEOLOGY OF SECTION B, SAN LUIS DIVISION. 



Section h covers considerably more ground than the preceding one. 

 The eastern boundary is formed by the easterly limits of the district as- 

 signed j the northern one, by the Arkansas Eiver; the western, by Pon- 

 cho Pass and the western borders of San Luis Valley ; the southern, by 

 the southern limit of the district. Orographically, this section is sepa- 

 rable into four natnral divisions: 1. The heavy massive granite mount- 

 ains, with the Wet Mountains to the east; 2. Wet Mountain Valley, 

 at the western border of them ; 3. The Sangre de Ohristo range, divid- 

 ing it from; 4. San Luis Valley. The character of the southern con- 

 tinuation of the Front range presents but little variation from that given 

 in the preceding section. Some differences are occasioned by the thick- 

 ening of the Jiesozoic beds farther south, and the range is devoid of 

 those characteristic little groups exhibited farther north in the Garden 

 of the Gods. As arule, the bluffs rising east of the termination ofthegran- 

 itic range are higher and more bulky; their appearance remaining very 

 similartothosefarthernorth, however. Althoughneverrisingtoany very 

 considerable altitude, the granitic mountains of the Front range present 

 a heavy aspect ; deep, and frequently quite rough, canons intersect the 

 country. 



Toward the western and southwestern portions of thisbnlky range, a 

 long narrow strip of trachyte occurs, varying somewhat the character; 

 single high peaks appear, accompanied by the well-known high narrow 

 plateaus. Little parks are dispersed throughout these mountains. Wet 

 Mountain Valley might be called one of the larger parks, extending 

 along the east base of the Sangre de Christo range. This range rises 

 abruptly from the valley to an altitude of 12,000 to 14,000 feet absolute 

 height, giving it a relative one of 3,000 to 5,000 feet. Following in its 

 conrse an almost straight line for forty miles, it presents altogether a 

 very imposing sight. The average width of the Sangre de Ohristo range 

 is not much over ten to twelve miles, which, compared with its length 

 and relative altitude, is small ; and as the color of the rocks composing 

 the mountains is dark, the range appears to very good advantage. 



A naked and sharp appearance is presented by the peaks of this 

 mountain-range. Extending beyond the timber-line, their highest 

 slopes are composed of loose rocks, usually with steep descent into one 

 of the canons formed at the side of the highest i:)oints. 



San Luis Valley slopes off gradually west from the Sangre de Christo 

 until its lowest point is reached almost in the middle; then it rises again 

 just as gradually to the westward. 



Granite, as in section «, forms the chief bulk of the mountains in sec- 

 tion h. It occurs mainly in an immense wedge-shaped mass, beginning 

 at the Arkansas Eiver and extending onward to the southeast until at 

 last it pinches out there. Its eastern boundary is determined by the 

 boundary of the Front range, its western partly by the base of the 

 Sangre de Christo, farther south by the border of Wet Mountain Valley. 

 At Poncho Pass, the northwestern limit of section &, the granite is found 

 extending over from the west. 



Granite of a different character and different appearance forms the 

 center of the Sangre de Christo. It crops out all along the crest of the 

 range', so far as could be determined, with the exception of a single 



