GAKNETT.l CULTIVABLE AREAS OF SAN LUIS VALLEY. 329 



this valley is as flat as a billiard-table. Variations of level are very 

 slight, and are imperceptible to the eye. The beds of the streams are 

 but slightly depressed below the level of the valley, generally but two 

 or three feet. Most of the soil is sandy, especially toward the eastern 

 side, where the sand is heaped up into dunes, against the mountains, and 

 toward the south, while northward the sand decreases, and the soil be- 

 comes an adhesive clay. 



San Luis Creek heads in the northern end of the park in a small sub- 

 valley known as Homan's Park. In its southward course it is joined 

 by numerous little tributaries from the Sangre de Cristo Range, on the 

 east. Most of these little streams sink in the porous soil in the summer, 

 but each sufnces to irrigate a small patch of ground at the foot of the 

 mountains. 



From the west, Kerber and Sawatch Creeks join San Luis Creek. The 

 former has a few square miles of fine meadow-land along its coarse. 

 The latter, a large creek, has fine, broad, meadow-like bottoms in the 

 park, and a broad valley accompanies the creek 15 or 20 miles into the 

 mountains. On this and the main stream, San Luis Creek, there are 

 very large arable areas, compared with the apparent size of the creeks. 

 From percolation through the soil, most of the bottom-land is more or 

 less marshy, i. e. naturally irrigated. 



This drainage system (of San Luis Creek), which includes the north- 

 ern half of the portion of San Luis Valley, which we are considering, is 

 not tributary to the Eio Grande, but, flowing down the valley near its 

 eastern border to a point opposite the debouchure of the Eio Grande, it 

 spreads out into an extensive swamp, having no outlet, save evapora- 

 tion, overgrown with luxuriant greasewood, and developing here and 

 there into small lakes or ponds, the water of which is a strong solution 

 of alkali. 



The Rio Grande heads in the heart of the San Juan Mountains. From 

 the great snow-fields and the abundant showers which fall on these high 

 mountains the stream grows rapidly, and at its entrance into San Luis 

 Valley it is one of the largest streams of the State. From the point of 

 entrance into the valley its course, which heretofore has been nearly 

 east, gradually turns to south as the river slowly sweeps out into the 

 middle of the valley. It has several good-sized tributaries in the val- 

 ley, Alamosa and La Jara Creeks, and the Conejos, with its branch, the 

 Eio San Antonio, from the west, and the Trinchera, Culebra, and Cos- 

 tilla from the east. Many more streams come down from the mountains 

 to the edge of the valley, but are absorbed by the hot sandy soil. 



The mountains on all sides are high, and send down a large amount 

 of water into the valley, but the character of the soil is such that much 

 of it is immediately absorbed. 



The agricultural capabilities of this valley are measured solely by the 

 supply of water. Were there a sufficient supply of that liquid, the 

 whole valley could be made productive. 



Prof. Cyrus Thomas, in the annual report for 1870, page 198, esti- 

 mates the irrigable land at 25 per cent., without the use of reservoirs. 

 In this estimate I agree with him. The amount of water which enters 

 the valley north of the line of New Mexico, including the Eio Grande 

 (which is by far the largest stream), will irrigate 1,291 or nearly 1,300 

 square miles. This is very nearly all the water which enters the valley. 

 The irrigable area, then, 1,300 square miles, is practically the entire 

 irrigable area of the whole valley, and is about 25 per cent, of the en- 

 tire area. I, however, suppose all this water is used in that part of the 



