200 GEOLOGICAL SURVEY OF THE TERRITORIES. 



which is often noticed in comparing the climate of open plains with that 

 of adjacent mountain valleys. 



Should the time come when there will be an urgent demand for land 

 in this vicinity, an encroachment could be made upon the marshy bor- 

 ders of the central basin, which if redeemed would afford several thou- 

 sands of acres of rich soil. 



On the southwest this basin is bordered by a somewhat elevated, 

 gravelly plateau, varying in width from eight to fifteen miles, which, 

 beginning at the mountains on the west, passes eastward between the 

 Eio Grande and Gareta round the south end of the basin, separating it 

 from the Eio Grande bottoms. In regard to the possibility of irrigating 

 this ridge I will speak hereafter. 



The Eio Grande, rising in the mountains to the west, flows directly 

 east until it reaches the middle of the valley, where, making an abrupt 

 bend, it runs south through the entire length of the valley, dividing it 

 into nearly equal parts. On the east side, between the Sahwatch basin 

 and the Eio Costillo, lies a broad, slightly-inclined plain, averaging 

 about twenty miles in width. It is interrupted, in its southwest por- 

 tion, by a mesa of considerable extent, and by occasional foot-hills which 

 shoot out from the mountain on the east. The southern half is undulat- 

 ing, but the northern portion is composed of three levels : first and low- 

 est, the river bottom, some five or six miles wide ; the second correspond- 

 ing with the plateau before mentioned, and which occupies the region 

 about Fort Garland, having an area of one hundred and fifty or two 

 hundred square miles ; the third, which is the highest, lying south of 

 the second. The bottoms along the Eio Grande are composed of deep 

 rich soil, generally covered with tall grass, or thickets of bushes, with 

 here and there open groves of cottonwood. They can, without much 

 difficulty, be irrigated from the river, but I am of the opinion (and on 

 this account have been thus minute in my description of this locality) 

 that, by commencing a canal where the river emerges from the mount- 

 ains, and bringing it along the plateau and around the bend upon the 

 second level, not only the plateau and a great portion of the second 

 level, but the southern slope of Sahwatch basin and Eio Grande bottoms 

 might all be irrigated from it. It is possible there may be a depression 

 between the Eio Grande and Gareta at the upper portion, which would 

 necessitate the building of an aqueduct, and thus increase the expense, 

 but in regard to this I cannot speak positively. This canal would irri- 

 gate at least five hundred thousand acres, at a moderate cost per acre. 



From the Trenchera most of the eastern portion of the second level 

 can be irrigated 5 and it is possible a portion of the higher level might 

 be reached by water from this stream and the Culebra, near their 

 sources in the mountains. 



An old Mexican claim extends over a considerable portion of this part 

 of the valley. Eeaching from the south end of the Sierra Blanca to the 

 Eio Costillo, it embraces the entire valleys of the Trenchera, Culebra, 

 and Costillo, amounting to one million three hundred thousand acres. 



The Eio Culebra furnishes one of the prettiest and richest valleys of 

 this section, its chief expanse being along the eastern margin near the 

 mountains, from which numerous little tributaries pour down their cool, 

 clear waters. This expanse, lying between the mountains on the east 

 and the " cerillos" on the west, has been very appropriately designated 

 the "vegas" or meadows, on account of the luxuriant growth of grass 

 that covers its soil. There is quite a settlement here, chiefly Mexican, 

 aud a large portion of the valley at this point is already under cultiva- 

 tion. The county seat of Costillo County, San Luis, (or Culebra,) is lo- 



