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<br />the basin expands under the impetus of good power and good water supplies, <br />I foresee thai industries will spring up 'fith their attendant communities. <br />Based upon past experience, many of th~se new developments will need <br />flood control. The Corps of Engineers latands ready to assist in satisfying <br />that need. <br /> <br />******* <br /> <br /> <br />TREE RINGS ANn WATER <br />Bryant Bannister <br />Laborat,ory of Tree-Ring Research <br />University of Arizona <br />Tucson, Arizona <br /> <br />One of my first visits to this part of the country was some ten years <br />ago as a member of an archaeological e,xpedition engaged in the excavation <br />of a small cave about 14 miles downstrllam from Hoover Dam on the Arizona <br />side of the COlorado. <br /> <br />Among other things found in the cave were some broken bits of <br />pottery (potsherds) easily identifiable as having been manufactured in some <br />of the larger prehistoric settlements in the Flagstaff region. Fortunately <br />we know the period of manufacture of this pottery since the settlements <br />where it originated have been dated by means of the wooden beams used in <br />their construction. By inference then, !we were able to date the period of <br />occupancy of this small cave on the Colorado River. The means by which <br />this dating of wooden beams was accomplished was through tree-rings, the <br />science of dendrochronology, more popularly known, perhaps as "tree-ring <br />dating". It is my intention to tell you how the tree-ring method works, why <br />it works, the significance of the data derived, and some of the more mean- <br />ingful results - meaningful, at least, in terms of past precipitation and run- <br />off histories. <br /> <br />First, how does the tree-ring njethod work? I think I can safely <br />assume that nearly everyone here has ~een the rings in trees, either on the <br />tops of stumps, on their cross-section~, or even on the ends of commercially <br />cut lumber. The concentric rings are ordinarily readily visible. In the <br />species of trees with which we primarily deal, that is the western conifers <br />such as ponderosa pine, Douglas fir, pinyon pine, and a few others, the tree <br />characteristically puts down one new ring each year -- hence the annual ring. <br />Another very important characteristic bf some trees is that the rings vary in <br />size. Some are thick, some are thin, ~hile most are of average size. In <br />looking at a ring series of this type, oI\e is immediately aware of ;the ring <br />patterns formed by the sequence of thicjk and thin rings. We say that this <br />type of ring series has "character". If you were to go into the field today <br /> <br />- 12 ., <br />