30 GEOLOGICAL inSTOKY OF LAKE LAHONTAN. 



the western rim of the Great Basin, and was determined by the crest line 

 of the Sierra Nevada, from the eastern slope of which the laki; received its 

 greatest tribute. The Walker, Carson, and Truckee rivers gathered the 

 surface drainage of the mountains into previously excavated channels, which 

 bear witness to a long period of erosion antecedent to the existence of the 

 Quaternary lake. The divide between the waters that flowed into Lake 

 I.,ahontan and the drainage of the interior basins bordering it on the south 

 and east is extremely irregular, but is well defined throughout the greater 

 part of its coui'se by the crests of rugged mountains. 



The separate drainage systems into which the basin is divided are the 

 Humboldt and Reese river valleys of the east, Quinn River on the north, 

 the Walker, Carson, and Truckee rivers, together with Smoke and Buffalo 

 creeks, and Snowstorm and High-Rock canons on the west. The bounJar}- 

 of the region that drained into Lake Lahontan is shown on Plate IV. 

 Besides the areas draining into living streams there are several desert basins 

 within the Lahontan area, as represented on Plate XXIX. 



One of the most important conclusions to be derived from a study of 

 the drainage in the region of Lake Lahontan during the Quaternary period 

 is that the country at that time had about its present topographic form. 

 The mountains were then the same as we find to-day, excepting that the 

 lines carved by subaerial erosions are a little deej^er, the alluvial cones 

 about their bases are slightly larger, and they have undergone very mod- 

 erate post-Quaternary orographic movements. The canons occupied by 

 the tributaries of Lake Lahontan still afford drainage channels Avhen there 

 is sufiticiont precipitation to form, streams. If Quaternary man could revisit 

 his ancient hunting grounds, he would have no difficulty in recognizing the 

 landmarks that were once familiar to him. 'I'he mountains and valleys are 

 the same, although their scant}' \egetation li;is probably undergone many 

 changes. The great lakes which were familiar to him, however, have passed 

 away and given place to broad silent plains of desolation. The former 

 rivers have shrunken, and many of their channels are dry. 



