198 GEOLOGICAL SURVEY OF THE TERRITORIES. 



elliptical basin enveloping the sources of the Bio Grande." Its entire 

 length, in a direct line from the summit of Poncho Pass to the mouth 

 of the Bio de Taos, is about one hundred and fifty miles, and its great- 

 est width, counting from the crest of the rim, about one hundred miles; 

 but its surface area cannot properly be estimated at more than one hun- 

 dred and forty miles long, by an average width of sixty miles, giving an 

 area of eight thousand four hundred square miles. Of this amount 

 perhaps one-fourth, or about one million three hundred and fifty thou- 

 sand acres, can be irrigated and brought under cultivation by ordinary 

 means, and by damming up and drawing off in canals the waters of the 

 Eio Grande the area of cultivable land may be expanded above these 

 figures. 



The mesa plains, mountain foot-hills, and slopes afford nutritious 

 grasses suitable to the pasturage of sheep and cattle. The average ele- 

 vation of the surface is about seven thousand feet above the level of the 

 sea. 



The northern part of this section is occupied by an isolated basin of 

 considerable extent, to which the name San Luis Park is sometimes lim- 

 ited ; it is also called the " Bincon," and " Sah watch Basin." The waters 

 of this basin, instead of entering the Eio Grande, are poured into a reser- 

 voir near the western base of the Sierra Blanca, which has received the 

 name Sah watch Lake. For a long time the very existence of this lake 

 was a matter of doubt, and even at the present day, with settlements 

 beginning around it, its extent is a matter of dispute, the estimates vary- 

 ing from three to sixty miles. I cannot describe this singular basin and 

 reservoir in any better manner than by quoting the language of the 

 United States geologist, (chief of our expedition,) found in his prelimi- 

 nary report of last year : " This northern portion [of the San Luis Valley] 

 above the bow of the Bio Grande is about sixty miles in length, and has 

 an average width of fifteen or twenty miles. About the ceuter (rather 

 in the southeast part) of this park is a singular depression, about ten 

 miles wide and thirty miles long, which looks like one vast thicket of 

 grease-wood (Sarcobatus vernicularis) and other chenopodiaceous shrubs. 

 Into it flow some twelve or fifteen good-sized streams, and yet there is 

 no outlet, neither is there any large body of water visible. It seems to 

 be one vast swarap or bog with a few small lakes, one of which is said 

 to be three miles in length. Although disconnected from any other 

 water system, the little streams are full of trout." 



The boggy nature of the broad margin, the shallowness of the streams 

 where they enter it, and want of interest on the part of those residing 

 in the vicinity, have probably prevented an examination sufficient to 

 determine, with any degree of accuracy, the extent of the lake or lakes 

 contained therein. During the spring and early part of summer the 

 streams which run into it must carry down a large amount of water, 

 part of which probably sinks into the margin which has dried during 

 the autumn, the rest evaporating into the dry atmosphere. The streams 

 on the east side generally dry up in the latter part of the season, but 

 those on the west and north are constant runners. 



Commencing at Poncho Pass on the northern extremity of the section 

 and moving southward, we enter the valley of Homan's (or San Luis) 

 Creek, which expands for a part of its length into what is called Homan's 

 Park. This is about four or five miles wide at its broadest part, and 

 some seven or eight miles long. The arable portion, which lies chiefly 

 on the west side, although somewhat inclined, can be easily irrigated 

 from the little streams which descend across it to the principal chanuel. 

 The soil, though mixed with coarse sand, is quite good, and will produce 



