170 GEOLOGICAL SURVEY OF THE TERRITOELES. 



hundred feet in height. I know of no finer exhibition of these marls in 

 their thickness, or their architectural style of weathering. On the 

 north side of the creek, the granites project up through the marls. 



The raoun';ains near the source of the Eio Trampas are very lofty, 

 with some high peaks which are rounded with dome-like tops, one of 

 which is called" Old Baldy"from its bare summit. Where the foot-hills are 

 denuded of the drift or the marl, the red granites are exposed. Along the 

 base of the mountains, especially in the valley of the Pehasco there is a 

 great thickness of very coarse conglomerate resting upon the granite 

 horizontally. It undoubtedly is of the same age as the marl beds. In 

 the valley of the Pehasco there is a vast quantity of worn boulders, scat- 

 tered everywhere, similar to the valley of Boulder Creek in Colorado. 

 These worn rocks are of large size next to the mountain, but diminish 

 the further they recede to the westward. 



The valley of the Eio Grande is already settled by Mexicans wherever 

 there is an available spot. Nearly all the land that can be irrigated is 

 cultivated by them, and good crops are raised even with their rude style 

 of cultivation. 



CHAPTEE VIII. 



FROM TAOS TO FORT GARLAND. 



The valley in which Taos is situated may be said to be formed by a 

 notch or bend in the mountain range. On the southwest is the Pickaris 

 Eange, with a strike nearly northeast and southwest. The next range 

 east of this trends about north and south, and branching off from this, 

 north of the Taos Valley, are the Pueblo Mountains, Dos Mountains, and 

 the Eio Colorado Mountains, all with a strike nearly northwest and 

 southeast. The course of the Eio Grande is nearly south, and on each 

 side of Taos the small ranges of mountains run out near the river. The 

 notch or bow in this group of mountain ranges ahbrds a fine illustration 

 of the method of flexure in the mountain ranges. 



The Taos Valley is about eighteen miles in extent, from east to west, 

 and about sixteen miles from north to south. It is thickly settled by 

 Mexicans, and every avaihible spot of ground is taken up. 



The valley proper is scooped out of the Santa Pe marls, which must 

 at one time have prevailed extensively, as in the country north of Santa 

 Fe, but the surface has been smoothed off, so that nowhere are the marls 

 conspicuous ; still they can be seen all along the base of the mountains 

 bordering the valley where portions of the recent deposits lie high on 

 the mountain side. No sedimentary rocks of older date are seen, and 

 the Santa Fe marls rest directly on the metamorphic rocks. 



It is plain that the regular metamorphic rocks prevail in these mountain 

 ranges, but mingling with them in various localites are igneous out- 

 bursts, which have somewhat tinged the gneissoid rocks. A little south 

 of Taos Eiver we find beds of beautiful porphyritic breccia, which is 

 very compact, and is employed for building purposes. Westward, 

 toward the Eio Grande, it is x)robable that the broad level plain is 

 underlaid with a sheet of basalt, for the Eio Grande itself runs through 

 a very deep canon of this material for sixty-five miles, from La Joya to 

 the crossing of the road to Conijos in the San Luis Park. In all this 

 distance there is but one crossing for teams, and three others for persons 

 on foot, and there the passage is made with great difficulty. Far dis- 



