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, ,., to some bottom silt and dead storage plus considerable flood-control capacity on top of H to protect Yuma Valley in Arizona and the Imperial Valley in California and also in Mexico, is only about one-third enough 'to really smooth out these long-period averages. That is why we stress these shorter periods, as much as 10 years long wilhin the record, and much longer in earlier periods, WhICh really, with only Boulder Dam to rely on, dictate and control the amount of usable, available run-off." Mr. Elder was critical of the State Department for what he considered was a lack of gathering sufficient basic data on the Colorado River such as was done on the Rio Grande. One phase of such an investigation had to do with ground water. In answer to a specific question by Senator McFarland as to what additional data pertaining to the Colorado River he would want, Mr. Elder answered (pp. 501-502): "Mr. ELDER. One specific item that is much on our minds is the fact that large pumping possibilities, we know, are available across the line in Mexico, and an important resource of water supply is there that has not as y'et been wken into account or brought into the treaty negotiations at all, as iar as we can learn. "Senator McFARIAND. Of course, we have no way of getting that information. "Mr. ELDER. I myself have not, but the State Department, I am sure, does, and, in my opinion, should. "Senator McF ARIAND. Do you ha ve any idea how the flow of the river in regard to this matter could effect the amount of water that we would...le.Ld_own~t.o_M-,~xicD:; "Mr. ELDER. One possibility, probably even very likely,' is that heavy pumping across the border in future years might actually affect the amount of return flow that will be evident on the surface in the river immediate! y above lhe boundary, for any pumping just below the boundary could lower the general ground-water level there, and less relurn flow would be measurable to be credited lO the treaty. That is a little hard to explaLl with actual proof right now, but in your own Phoenix Valley pumping in many places is dOing just that, reducing the surface return flow in the Sa It and Gila Rivers. In any case, the pumping is an additior!al water source for Mexico that should b e a part of lhe whole treaty pic'ture, as its most benefiClal and advantageous use is for firming-up the run-off in wet years by pumping chiefly during drought periods. "Senator McFARIAND. I presume what you mean by that is that there is a WOlter level building up below which, as the water comes -36-