116 GEOLOGICAL UISTOEY OF LAKE LAIIONTAN. 



the nature of their material and the general absence of vegetation from 

 their surfaces serve to accent the topographic forms. 



Buffalo Springs are situated on the western border of the valley, at an 

 elevation approximately 25 feet above the playa and 300 feet below 

 the Lahontan beach. On Plate XX a portion of the border of the val- 

 ley is represented which extends from Buffalo Springs to an elevation 

 a short distance above the highest water line of the former lake. If the map 

 had been continued a mile or two westward, it would have shown a greater 

 portion of the sloping pediment of alluvium that surrounds the valley ; and it 

 extended for an equal distance east, it would- have embraced a portion of a 

 much gentler slope which finally merges with the playa in the bottom of the 

 basin. The alluvial slope represented on the map above the highest beach 

 shows a few of the numerous drainage lines which during the infrequent 

 rains conduct the surface Avaters to the bottom of the valley. The influence 

 of the beaches in deflecting the water-courses is indicated, as is also the 

 manner in which streams shift their channels, and sometimes bifurcate, on 

 alluvial slopes. 



The first feature to attract attention on inspecting this group of embank- 

 ments is the fact that they were built from the bottom iip. The oldest in the 

 series, so far as now exposed, is the lowest. The last formed is the Lahon- 

 tan beach. Another division in reference to age is also possible, as a por- 

 tion of the bars is coated with tufa, while other portions are free from 

 that deposit. On referring to the plate it will be seen that the lowest well- 

 defined beach occurs at a horizon 114 feet below the highest water line. 

 This is a gravel ridge, forming an irregular V-bar, from the apex of which 

 a somewhat curved embankment of gravel extends into the valley for about 

 half a mile. The projecting bar is coated with lithoid and dendritic tufa, 

 but the structures at a higher level are free from such deposits. The pro- 

 jecting bar has also suffered from erosion much more than those at a higher 

 level, and, besides, is coated with fine sediments. It thus appears that the 

 structures below the level of the lowest well-defined beach were formed be- 

 fore the deposition of the lithoid and dendritic tufas, while the bars and 

 beaches above that horizon were built at a subsequent date. From data 

 afforded at other localities we conclude that the construction of the higher 



