TOPOGEAPHIC FEATURES OF THE DESERT BASIXS. 29 



THE LO.N'G VALLEY BASIX. 



Long Valley lies just east of the Surprise Valley, beyond the crest of the gentle 

 anticline (?) already mentioned. It is a poorly defined valley the detailed structure 

 of which is very complex. On all sides it merges with the folded and dissected 

 lava plateau already mentioned. Its floor is an irregularly shaped playa dotted 

 with shallow and variable lakes, between which are very low and inconspicuous 

 divides. Several low passes lead out of the valley at about the same elevation, one to 

 the Coleman Valley (a tributary of the Warner Basin) and the others either to Duck 

 Flat or directly to the Surprise Valley. Without detailed examination it is not pos- 

 sible to determine which of these, if any, was a channel of ancient discharge. The 

 writer inclines to the opirdon that during the Lahontan period there was free or over- 

 flow discharge into Duck Flat and thence to the Surprise Valley, but this conclusion 

 can not be considered certain. The present lakes are fre.sh or brackish only. It is 

 not possihde to determine the yjresent drainage of each. The area of the whole vaUey 

 is about 775 square miles. 



THE ALVORD VALLEY. 



It will be recalled that the shallow syncKne of the Catlow and Guano VaUeys was 

 bordered on the east by the uplift of the Steens Moimtains. The eastern face of this 

 range is a high fault scarp, directly below which lies the Alvord Valley. Like the 

 Warner and Abert Valleys it is essentially monoclinal in structure, though an anti- 

 clinical structure pre'V'ious and parallel to the faulting has been detected by both 

 Russell and Waring. In the Steens Mountains this anticlinal structiu-e seems to be 

 entirely overshadowed by the much more profound monoclinal movement, but east- 

 ward from the Alvord Valley faulting and tilting have not been so profound and the 

 eastward di\'ide of the basin seems to be determined by the crest of one of the original 

 anticlines. To the south the basin reaches the less regular uplifts of the Pine Forest 

 Mountains and Trident Peak. It is separated from the Black Pock Desert only by 

 an alluvial di\'ide across the Pueblo Valley, but this di^dde is nearly a thousand feet 

 above the valley and is almost certainly pre-Lahontan. The northern extremity of 

 the Alvord VaUey is little known and it is possible that there may have been an outlet 

 to the ilalheur Paver, though the considerable salinit\" of the valley and the presence 

 of old strand lines around it would indicate the contrary''. 



The present bottom of the vaUey is cut by allu^'ial di^-ides into the subsidiary basins 

 of Ten Cent, Juniper, Mann, Alvord, and Tum Turn Lakes and that of the Alvord 

 Desert. All of these were covered and connected by the early lake and it is possible 

 that most of the others drained into that of the Alvord Desert for some time after 

 desiccation had begun. The White Horse Basin was also a former tributary and has 

 been cut off by the accumulation of alluvium and dune sand in Sand Gap, through 

 which it formerly discharged. 



The Thousand Creek and Virgin Creek Valley lying on the lava plateau east of 

 Long Valley, Nevada, seems to have been also a tributarv' of the Alvord and is now 

 separated thereform only bj' a low allu-\-ial divide in the gap north of the Pine Forest 

 Mountains. This valley has suffered greatly by stream decay and now contains 

 numerous local playas of small area and very recent origin. 



The areas of the various small basins into which the Alvord Valley is now divided 

 have not been computed in detail. Their total area, exclusive of the White Horse 

 Basin and the Thousand Creek Valley is about 1,600 square miles. The area of the 

 TMiite Horse Basin is about 300 square miles, and that of the Thousand Creek VaUey 

 1.300 square miles, making a total of 3.200 square miles for the drainage area of the 

 Alvord Basin during the Lahontan period. 



