54 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



Shakayuma. Here, below the mouth of the Rillito Wash, the broad, waste-filled basin of 

 the combined Rillito and Santa Cruz streams contracts to a narrow neck. On the south 

 the volcanic range of the Tucson Mountains projects into the plain, while about 2 miles 

 to the north the rocky foothills of the granite range of the Tortillitas rise from the alluvial 

 gravel. A buried dam of rock, so to speak, here crosses the Santa Cruz Valley beneath 

 the cover of alluvial deposits, causing the level of underground water to be relatively high 

 upstream from the point of the mountains, while downstream it rapidly falls. In the spring 

 of 1910 we found that the source of surface water nearest to Charco Yuma was 8 miles up 

 the Santa Cruz at the Nine Mile Water Hole; there the amount was sufficient for drinking 

 purposes, but not for any apprecial)le irrigation. Ranchers engaged in raising cattle 

 informed us that no water whatever had come down the river during the preceding winter, 

 although during the summer of 1909, when the rainfall amounted to almost exactly the 

 average quantity of 7 inches, floods came down after 15 to 20 showers. In some cases 

 the flow continued only 2 hours; in the height of the rainy season, however, a brook of 

 greater or less size flowed steadily for 2 weeks. The average duration of the floods was 

 about 36 hours. From this we infer that, during a summer of average rainfall, surface 

 water flows as far as Charco Yuma for about 30 days, during July or August. Socoro 

 Ruelas, a Mexican who in Ijoyhood and early manhood lived at the old stage station, one 

 of the cattle ranches at the Point of the Mountains, states that in winter water seldom 

 flows there. Even the heavy showers of summer sometimes fail to send any stream so 

 far down the valley. The nearest permanent source of water, as has been said, is at the 

 Nine Mile Water Hole, 8 miles away, but even this, he says, sometimes dries up, although 

 at other times (such as the late seventies or early eighties) water flows 2 or 3 miles from 

 it and has actually been used for irrigation. From the spring of 1885 to August 1887, 

 according to the Mexican, no water whatever came down as far as the Point of the Moun- 

 tains. In 1884, when Ruelas's father dug his well, water was struck at a depth of 28 

 feet; during the following dry j'ears the level fell below this, but water never absolutely 

 failed. In the winter of 1909-10 the level was 22 feet. I can not vouch for the dates 

 here given, but there can be no question as to the general accuracy of the facts. 



A talk with Mr. Langhorn, the station-master at Rillito, a mile or more north of the 

 old stage station and the Hohokam village, seems at first sight to put quite a different 

 aspect on the matter. Here a narrow strip of cultivated land extends along the railroad 

 for more than 3 miles. "Talk about dry farming," said Mr. Langhorn, "it's the easiest 

 sort of thing. Five inches of rain a year is all we need here. Just look at my fields. They're 

 not so good as usual, but they show what can be done even in a bad year hke this. It's 

 all in the way you plow and harrow and roll." A little investigation, however, soon 

 shows that the 300 acres here cultivated are provided with very effective irrigation, not 

 artificial, but natural. Because of the raising of the level of ground water in this particular 

 spot by the contraction of the vaUey, the moisture is nearer to the surface than elsewhere. 

 'When floods come down, water accumulates in pools. Mr. Langhorn pointed out patches 

 in which the barley was then particularly fine, but wliich can not be planted in some years 

 because of the moisture. Even in bad seasons these fields are much wetter than any other 

 place for many miles. The winter of 1909-10 was by no means propitious. Although the 

 rainfall amounted to only a little less than the average, it v/as badlj^ distributed, most of 

 it falling early in the winter. Accordingly the grain planted in September and October, 

 and even in early November, grew fairly well, while that planted after the middle of No- 

 vember failed to head. Even in the best part of the 300 acres available for cultivation 

 in this district, the hay crop, for which the barley is planted, was expected to amount to 

 only about 15 tons, although in the preceding year it had been 95. This particular area 

 has not been cultivated long, and its possibilities in really dry seasons have not been tested. 

 At least a quarter and possibly a third of the winters in the last 43 years have been 



