GA^NNETT] CULTIVABLE AREAS ON SOUTH PLATTE DRAINAGE. 615 



irrigate 218 acres, or that three cubic feet per second will irrigate a 

 square mile, we shall find that the area irrigable by the South Platte is 

 933 square miles. Of this G24 square miles are in the plains and 311 

 square miles in the mountains, of which more hereafter. This plains 

 area includes all the bottom-lands on the South Platte within the State, 

 and also a part of the bench-land bordering the stream. I have little 

 detailed knowledge of the bottom-lands of the river below Greeley, but 

 presume that they keep pretty uearly the same average width as above 

 this point. Above Greeley they are from half a mile to a mile wide, 

 spreading out to three, four, or five miles at the mouths of some of its 

 branches, making an average of about two miles in width, as was stated 

 above. 



The irrigating capacity of the branches of the South Platte from the 

 west below the foot of its caQon, *. e., in the plains, I estimate to be 

 nearly equal to that of the South Platte itself, or, in figures, the amount 

 of water carried by them is about 2,400 cubic feet per second, which 

 represents an irrigable area of 800 square miles. Of these, the Cache 

 la Poudre and its branch, the Box Elder, can irrigate 174 square miles, 

 a large part of which is near its mouth, where, in the neighborhood of 

 the town of Greeley, the bottom-lands spread out to a great width. 

 Along the Big Thompson there is an irrigable area of 116 square miles; 

 along the Little Thompson, 44 square miles. Saint Yrain's Creek can 

 irrigate 174 square miles, half of which can be effected by the main 

 stream, and half by its two branches, Boulder and Coal Creeks. Clear 

 and Ralston Creeks can water 234 square miles; Bear Creek, 68 squure 

 miles. Of the streams which enter the South Platte from the South, 

 Cherry and East Plum Creeks head in the Arkansas divide and carry 

 but little water in proportion to the size of their valleys. The irrigating 

 capacity of each of these is estimated to be 44 square miles. 



West Plum Creek heads in the mountains and carries more water 

 than these latter streams. Its irrigable area is estimated to be 72 square 

 miles. 



The courses of the branches of the South Platte, from the westward, 

 in the mountains are almost entirely in canons or narrow valleys. They 

 contain no cultivable areas of any extent. Space for a ranch or two is 

 found here and there ; but, altogether, they are not of sufficient import- 

 ance to be mentioned in this connection. 



The following measurements of the amount of water carried by Clear 

 Creek, at Golden City, were kindly furnished me by Capt. E. L. Berthoud, 

 of the School of Mines, of that place : 



Cubic feet. 



September 3. — Amount of water carried 374 



August 27. — Amount of water carried 536 



June 19 (flood height). — Amount of water carried 1, 765 



South Park is a table-land, very uniform in surface, with the excep- 

 tion of a few minor ridges, which traverse it in a direction slightly east 

 of south, and in the southern part numerous volcanic buttes. Its shape 

 is nearly elliptical, its longer axis being nearly north and south. Its 

 length is about 50 miles and its width 25 miles. The area is about 870 

 square miles. The prevailing slope is from northwest to southeast. 

 The elevation is, in the northern and northwestern part, 9,500 to 10,000 

 feet ; in the southern part, 8,000 to 8,500. The mean elevation is not far 

 from 9,000 feet. 



The limits of the park are sharply defined by the mountains, which, 

 rise on all sides abruptly from the plains to the highest summits. 



