MiNDELEFF] ARTIFICIAL DEPRESSIONS. 245 



Tbe purpose of these depressions is not at all clear, and although 

 popularly known as reservoirs it is hardly possible that they were 

 used as such. The capacity of the Clear creek depression is about 

 100,000 gallons, or when two-thirds full, which would be the limit of 

 its working capacity, about 100,000 gallons. The minimum rate of 

 evaporation in this region in the winter months is over 3 inches per 

 month, rising in summer to 10 inches or more, so that in winter the 

 loss of water stored in this depression would be about 10,000 gallons 

 a month, while in summer it might be as high as ;?5,000 or even 40,000 

 gallons a month. It follows, therefore, that even if the reservoir were 

 filled to its full working capacity in winter and early spring it would 

 be impossible to hold the water for more than two months and retain 

 enough at the end of that time to make storing worth while. It has 

 been already stated, however, that these depressions are situated on 

 slight knolls and that the land falls away from them in every direc- 

 tion. As no surface drainage could be led into them, and as there is 

 no trace on the ground of a raised ditch discharging into them, they 

 must have been filled, if used as reservoirs, from the rain which fell 

 within the line that circumscribes them. The mean annual rainfall 

 (for over seventeen years) at Verde, a few miles farther northward in 

 the same valley, is 11'44 inches, with a maximum annual fall of 27-27 

 inches and a minimum of 4-80 inches. The mean annual fall (for over 

 twenty-one years) at Fort McDowell, near the mouth of the Rio Verde, 

 is 10'54 inches, with a maximum of 20-0 inches and a minimum of 4'94 

 inches.' 



If these depressions were used as reservoirs it is a fair presumption 

 that the bottoms were plastered with clay, so that there would be no 

 seepage and the only loss would be by evaporation. Yet this h)ss, in 

 a dry and windy climate such as that of the region here treated, would 

 be sufficient to render impracticable a storage reservoir of a cross sec- 

 tion and a site like the oue under discussion. Most of the rainfall is in 

 the winter months, from December to March, and it would require a 

 fall of over 12 inches during those months to render the reservoir of 

 any use in Juue ; it would certainly be of no use in July and August, 

 at the time when water is most needed, save in exceptional years with 

 rainfall much in excess of the mean. 



On the other hand, there is the hypothesis that these depressions 

 represent house structures; but if so these structures are anomalous in 

 this region. The contour of the ground does not support the idea of 

 a cluster of rooms about a central court, nor does the debris bear it out. 

 Mr. F. H. Gushing has found depressions in the valleys of Salt and 

 Gila rivers somewhat resembling these in form and measurement, and 

 situated always on the outskirts of the sites of villages. Excavations 

 were made, and as the result of these he came to the conclusion that 



'Report on Rainfall (Pacific coast and western states and territories), Signal OfHce tJ. S. War 

 Dept., Senate Ex. Doc. 91. 50th Cong., 1st Seaa., Washington, 1889; jjp. 70-73 (Errata, p. 4). 



