260 



GEOLOGICAL HISTOliY 0¥ LAKE LAHONTAN. 



evident that the entire Great Basin must have become tributary to the 

 ocean. Inclosed hikes of the present time are located in arid regions. 

 The lakes of humid regions invariably overflow. In arid countries the 

 water surf;xces of the lakes are small in comparison to the areas that they 

 drain; in humid regions the reverse is the rule. Lake Lahontan, as previ- 

 ously stated, was 8,422 square miles in area, and drained a region over 

 40,000 scjuare miles in extent; the water surface of the basin at the pres- 

 ent time is approximately 1,500 square miles. The Quaternary lake dur- 

 ing its maximum, uecupied approximately one-fifth of its hydographic 

 basin; at the present tjme only about one-twenty-sixth of the same area is 

 covered by water. From tliese data alone it will be seen that the present 

 is a time of desiccation in comparison to certain portions of the Quaternary. 

 Conq)aring Lake Lahontan with existing lakes in humid regions, we 

 find that its water surface was small in reference to its drainasre area. In 

 the case of Lake Superior, for example, the area of the lake is to the area 

 of its liydrographic basin as 1 to L72. The combined areas of the Lau- 

 rentian lakes is to their combined drainage areas as 1 to 3.19.*^ Could the 

 Laurentian lakes be inclosed, so that the only escape for their waters 

 would be by evaporation, it is evident that they would expand and occupy 

 a vastly larger part of their drainage areas than at present. In fact, the 

 mean annual evaporation in this region is -much less than the mean annual 

 rainfall, so that an inclosed lake would be an impossibility."'^ 



"In obtaining the data given above, the following table was compiled, which we insert for conven- 

 ience of reference. 



Areas of lakex and of their hi/drographic ImsitiK. 



Lakes. 



Superior 



Michigan (inclading Green B.ay) 



Hiirou {incluiiin^ Northwest Piissage 1,556, 



aud Geoi!;ian liay r.,626) 



Saint Clair 



Erie 



Ontario 



Combinefl areas 



Bonneville - . . - 



"Water areas. 



Square mile». 



30, 829 



21, 729 



9,033 

 7,104 



Hydro grraphic 

 areas. 



Square miles. 

 84, 961 



Katie of water i 

 area to hydro- 1 

 graphic area. 



1 to 1. 72 



1 to 2. 63 



s^Anu. Rep. Chief of Engineers, U. S. A., 1S69, pp. 645-648. 



