106 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



or move in height. On the western side of the valley this ancient water line 

 is rendered especially noticeable by the cliffs of deep purple that mark its 

 course. 



The narrow \alley in which Humboldt Lake is situated was a strait at 

 the time of the higher stages of Lake Lahontan, and connected the Carson 

 body of the former lake with the waters that occupied the northern part of 

 the Humboldt Valley. Li its topographical relations it was similar to the 

 constriction in the valley at the southern end of Winnemucca Lake, and is 

 paralleled in the Bonneville basin by the narrow passage, now known as the 

 Narrows of the Jordan, which connected the main body of Lake Bonneville 

 with the Utah Lake body. Li all these localities, and in many others 

 similarly situated that have been studied by the writer in the basins of the 

 extinct lakes of Utah and Nevada, the beach phenomena are greatly in- 

 tensified, and bars and embankments of gravel are unusually well displayed. 



At the southern end of Humboldt Lake a single embankment of 

 gravel from 50 to 125 feet in height" has been carried completely across 

 the valley in such a manner as to suggest that it is an artificial structure 

 intended to confine the drainage. At either end the main embankment 

 widens as it approaches the shore and forms heavy triangular masses of 

 gravel, on the surface of which appear many smaller bars built of clean, 

 well-worn shingle. These secondary bars form ridges with rounded crests 

 which vary from a few feet up to thirty or forty feet in height, and are 

 nearly level-topped for long distances. These are seldom straight, but 

 curve with beautiful symmetry, each gracefully bending ridge marking the 

 course of a current in the watei's of the ancient lake in which it was formed. 



The main embankment, i. e., the one crossing the valley, declines gently 

 in height from either end towards the center, and has been cut through at 

 its lowest point by the overflow of Humboldt Lake. The gap carved by 

 the outflowing waters is shown in the profile at the bottom of Plate XVIII. 

 The diagram was constructed from a line of levels run from the Lahontan 

 beach on the Niter Buttes to the highest water line on the west side of the 

 valley; the points selected for the i)eginning and the end of the line were free 



^'The base of this structure is deeply buried beneath lacustral sediments ; the figures given above 

 indicate its elevation above Humboldt Lake. 



