360 REPORT UNITED STATED GEOLOGICAL SURVEY. 



valley wbich is in Colorado, and thus increase the proportion of irrigable 

 area to 32.5 per cent, of that portion of the valley. 



This area is apportioned as follows among the different streams which 

 enter the valley. The Eio Grande carries at the end of the irrigating 

 season not far from 2,500 cabic feet of water per second. In that part 

 of its course above the San Luis Valley there is but little irriga- 

 ble land. There is a small area in Antelope Park, bnt it is too high 

 for any but the hardiest crops to flonrish. Below this the valley is nar- 

 row, and the amount of water used for irrigation would be so small that 

 it need not be taken into account. 



Our previous supposition, that one cubic foot of water per second will 

 suffice to irrigate 218 acres, will not hold good in the case of the Rio 

 Grande drainage area in this valley, for the soil is of the sandiest, and 

 the waste of water would be enormous. Instead of allowing 3 cubic 

 feet per second to the square mile, I should judge that 5 cubic feet 

 would be none too much. This would give an iirigable area of 500 

 square miles by the river, and by its branches as follows: Alamosa and 

 La Jara, 100 square miles; Conejos, about the same; the Trinchera, 

 72 square miles ; the Culebra, 58 square miles ; the Costilla, 29 square 

 miles ; and the Gata, 15 square miles. 



Profile of the Eio Grande from Us head to the foot of Taos Canon. — (Hayden.) 



From head 



Elevation. 



Fall per 

 mi e. 



Head in Cunningl.am Pass . 



Mouth of Polo Creek 



Mouth of Lost Trail Creek . 



-Antelope Park 



Del Norte 



lu San Luis Valley 



Do ^ 



Foot of Taos Cauon 



Miles. 



4.5 

 1:5.0 

 28.0 



Sr'.O 



IIH.O 

 148.0 



Feet. 

 li, 0?0 



10, 7ro 



9, 590 

 8,900 

 7,890 

 7,574 

 7,415 

 7,301 



Feet. 



228. 9 

 141.1 

 40.0 

 18.3 

 10.5 

 5.3 



DRAINAGE AREA OF THE SAN JUAN RIVER. 



The San Juan drains the southern slopes of the San Juan Mountains. 

 The headwaters of the main stream and most of its branches have long 

 southerly courses in the mountains, where their valleys are narrow, and 

 flanked on each side by high mountain spurs. The drainage area in 

 Colorado is but 5,600 square miles, and this is, in large part, composed 

 of the poorest country in the State. In and near the mountains the 

 land is good and water abundant, but away from them, on the south 

 and west, it is arid and desert. There is no water in the country, 

 except in the main river, and a few insignificant holes and springs. 



Most of the course of the San Juan itself through the arid and desert 

 plateau is in New Mexico and Utah, as are also the lower courses of the 

 more important branches. 



In this drainage system there are, it is estimated, 392 square miles of 

 irrigable land, distributed in narrow belts in and near the mountains. 



On the Eio Navajo, the most eastern branch, there are a few square 

 miles of irrigable valley, extending from near the foot of Banded Peak 

 to the south line of the State. 



The main stream (San Juan) has a fine valley, one to two miles in 

 width, extending from the mouth of Caiion Creek to a point below that 

 of the Eio Piedra, a distance of nearly 50 miles. The Piedra, below the 



