64 BUEEAU OF AMERICAN ETHNOLOGY [bull. 54 



Still, the cutting of all the canyons long antedated human occu- 

 pancy of the region, and the streams had probably shrunken much 

 from then* former condition before the human mvasion. 



Geologic evidence leaves no doubt that the Southwest had a 

 climate more humid during part of Pleistocene time than at present. 

 Lakes with outlets do not fluctuate much in depth or area, because 

 during more himiid periods the surplus water is carried off by the 

 outlets. Land-locked lakes, on the other hand, vary greatly with 

 fluctuating climatic conditions and constitute an excellent mdex of 

 those conditions. At present in the Great Basin evaporation bears 

 such ratio to precipitation that no very great lakes are in existence 

 or can exist.^ It is evident that durmg part of the Pleistocene 

 period that ratio was different, for then lakes of great size covered 

 portions of the basin and passed through at least two great periods 

 of extension and contraction and probably several minor ones. 

 The best known are Lake Bonneville and Lake Lahontan,^ though 

 many others are known which are now either dry or occupied only 

 by small shallow saline or alkaline lakes. Lake Bonneville, now 

 represented by the much shrunken Great Salt Lake, then extended 

 over the greater part of what is now western Utah and eastern 

 Idaho and Nevada, with a depth of nearly 1,000 feet at one time. 

 Lake Lahontan, now represented by Humboldt, Pyramid, Carson, 

 Walker, and other small lakes, then covered a large part of what 

 is now northwestern Nevada and extended into California. It is not 

 necessary to suppose that this lake period was one of very great 

 humidity; indeed, it probably was not, otherwise all of the lakes 

 would have overflowed the rims of their basins and established 

 outlets, whereas only part of them succeeded in domg so, and only 

 at the highest stage. However, it is certain that the climate must 

 have been more humid than now. It appears, then, that since late 

 Pleistocene time there has been a change of climate, but the time 

 can not be reckoned in a few years or even a few centuries. The 

 maximum extension of these lakes was many thousand years ago, 

 but theii- desiccation, with the accompanying minor fluctuations, 

 must have consumed a long period, extending to a much more 

 recent time. Some of the remnants of these anpient lakes have 



1 Davis, Arthur P., The New Inland Sea, in Nat. Geog. Mag., xvin, 44, 1907; Henry, Alfred J., Sal- 

 ton Sea and the Rainfall of the Southwest, in Monthly Weather Review, U. S. Weather Service, xxxiv, 

 557-59, 1907; Nat. Geog. Mag., xvm, 245, 1907; Bigelow, Frank H., Studies on the Rate of Evapora- 

 tion at Reno, Nevada, and in the Salton Sink, ibid., xix, 23, 1908. 



2 Gilbert, G. K., Contributions to the History of Lake Bonneville, in Second Ann. Rep. U. S. Geol. Surv., 

 for 1880-Sl, pp. 107-200, 1882; Lake Bonneville, Monogr. U. S. Geol. Surv., I, 1890; Russell, Israel C, 

 Sketch of the Geological History of Lake Lahontan, a Quaternary Lake of Northwestern Nevada, in Third 

 Ann. Rep. U.S. Geol. Surv., for 1881-8S,j)p. 189-235, 1883; Geological History of Lake Lahontan, a Quater- 

 nary Lake of Northwestern Nevada, Monogr. U.S. Geol. Surv., xi, 1885; A Geological Reconnaissance in 

 Southern Oregon, in Fourth Ann. Rep. U. S. Geol. Surv., for 1882-8S, pp. 431-64,1884; Quaternary His- 

 tory of Mono Valley, California, Eighth Rep., for 1886-87, pt. I, pp. 261-394, 1889; King, Clarence, Lake 

 Lahontan, in U. S. Geol. Surv. iOth Parallel, I, 504-30, 1878. 



