112 GEOLOGHOAL HISTOEY OF LAKE LAHONTAX. 



northern face of the Mopung Hills was also formed by the same displace- 

 ment. The greater part of the orographic disturbance in this region took 

 place previous to the rise of Lake Lahontan, and gave origin to the main 

 features in the structure of the basin now occupied by Humboldt Lake. 

 Movements must have taken place along this line of fracture during the 

 iuter-Lahontan time, as is indicated by sloping terraces on the western face 

 of the Niter Buttes. Since the withdrawal of the waters of the former lake 

 the fault at the immediate base of the west Humboldt Range has increased 

 its displacement 50 or 60 feet, and formed fresh scarps in Lahontan gravels 

 (see Plate XLV). There has also been some recent movement in the branch- 

 ing faults about the base of the Niter Buttes, which may be traced for a 

 considerable distance across the alluvial slopes to the westward, and appears 

 again at the base of the Mopung Hills. The displacements, noticed above 

 in explanation of the accompanying map, will receive further attention in 

 Chapter X, which is devoted to post-Quaternary orography. 



EMBANKMENTS ON THE SOUTHEKN BOEDER OF THE CARSON DESERT. 



On the south shore of South Carson Lake there stands a bold, rugged 

 promontory of basaltic rock that is girdled with terraces and incrusted with 

 tufa about its base. During the existence of Lake Lahontan, this butte 

 formed a high, rocky island, that was separated from the mainland to the 

 southward by a narrow strait, pai'tially obstructed by small islands, through 

 which the currents must have swept with great force. On the southern or 

 mainland border of the strait, the group of gravel bars represented on 

 Plate XIX were formed. 



The changes wrought by waves and currents are marked with unu- 

 sual distinctness all along the southern margin of the Carson Desert. 

 This was the shore of the largest open water area of the former lake, 

 and was exposed to the full force of storms from the north. The con- 

 spicuous sea-cliff on the southern margin of the Carson Desert may be 

 followed all the way to the pass near Allen's Springs, where it is bold 

 and rugged, as represented by the heavy liachuring at the top of the 

 accompanying plate. During the higher stages of the lake the currents 

 swept southward through the pass, carrying with them the debris of the sea- 



