92 GEOLOGY. 



We learn from the report of Captain Beckwith, United States army, how very circumscribed 

 is the area of land which is now susceptible of cultivation in the Desert, and the fact that 

 families sometimes go a great distance from the settlements for the advantage of obtaining a few 

 acres of ground susceptible of cultivation. (See page 65, vol. I, Pacific Railroad Report.) 

 When the truth comes to be admitted, I think it will be found that the upper valley of the Rio 

 Bravo, embracing New Mexico and a small portion of western Texas, is the only tract of land, 

 within the limits mentioned in the preceding paragraph, where a body of land is to be found 

 susceptible of sustaining any considerable population. And yet we see, since our occupation of 

 that Territory, in 1846, the population has increased but little, if at all. 



[EXTRACT FROM REPORT OP ASSISTANT ARTHUR SCHOTT.] 



TERTIARY SHORE OF THE DESERT. 



Vallecito, another small Indian settlement in a valley with a number of brackish springs' 

 and abounding in saline soil, is situated on the upper edge of the Desert shore. From Vallecito 

 the road continues along the dry bed of a mountain torrent, deeply filled in with shifting sand. 

 This sand stream seems to form one of the heads of Oarrizo Creek, and winds through dreary 

 flats, flanked on both sides by the naked, desolate slopes of the primary and metamorphic 

 mountains. The latter finally cease, and Tertiary ridges, supported by dark masses of eruptive 

 rocks, take their place. These form the real edge of the Desert ocean, which, no doubt, was 

 once the bottom of a wide salt-water basin. The washing of tidal oscillations upon this bold 

 shore caused, probably, the dune-like deposition of the Tertiary hills along the foot of the 

 western Cordilleras. To confirm this supjiosition of their origin, an isolated group of seabeach- 

 loving palms appear to the left of the road, near Carrizo Creek, marking, at the same time, a 

 spot with permanent water. A brief but graphic description of those Tertiary ridges and 

 hillocks has been brought before the public in Major Emory's report of 1848.— (See page 103.) A 

 sketch of these hills is herewith given. 



VOLCANIC VENTS. 



Among the Tertiary ridges and hillocks, one may be recognized at once by its singular shape, 

 appearing to be the vent of some volcanic activity now silenced. Major Emory, according to 

 our knowledge, set forth, prior to any other writer, the supposition of the true nature of these 

 hills. After close examination we are able to corroborate the correctness of that supposition. 

 Another not less convincing proof of its neptuno-volcanic origin may be sought in its geo- 

 graphical position, which is upon that long volcanic seam, running north and south, and lining 

 the eastern base of the Peninsular Cordilleras, parts of which are still in activity. 





TERriCAL SECTION OF AN EXTINCT CRATER IN THE TERTIARY FORMATION, BORDERING THE EASt'sloPE OP THE CALIFORNIAN CORDIMRAS. 



