26 BULLETIN 54^ U. S. DEPARTMENT OF AGEICULTURE. 



THE ALKALI LAKE BASIN. 



The Alkali Lake Basin is essentially a northward extension of the Abert Lake 

 trough and is separated therefrom by the region of local cross uplift in the vicinity of 

 Euchre Butte. On the east the basin is bordered, like Abert, by the scarp of an east- 

 ward dipping monocline which merges toward the north into the less simple uplifts 

 of Little Juniper and A^'agontire ]\Iountains. To the west the basin is separated from 

 the Christmas Lake and Summer Lake Valleys by the usual inconspicuous divide 

 across the lava plateau. It appears that the lake once received from this direction a 

 main tributary which drained the pans and valleys of the lava plateau north of Sheep 

 Rock. This drainage line has now been cut off almost entirely, and the lava plateau 

 has been divided into numerous local basins. 



The deepest depression of the valley is Alkali Lake, a playa lake of very variable 

 size. In the dry season it is usually reduced to three or four saUne ponds occupying 

 wind-eroded depressions in the playa. (PL III, fig. 2.) The northern extension of 

 the Allcali Lake Valley, called "North AlkaH," is now cut off from the main valley 

 by a dam of wave and dune sand and has become somewhat saline. However, this 

 .separation is quite recent and does not affect the unity of the valley. A series of 

 terraces about both North and South Alkali Valleys indicates previous occupation by 

 a considerable lake, and, as all . divides are far above these terraces, the lake must 

 always have been inclosed. The drainage area of the lake was about 400 square 

 miles, which has been reduced to perhaps a third of this value by the cutting off 

 of North Alkali and of the pans of the plateau. 



■ THE WARNER BASIN. 



Mention has aheady been made of the eastward-dipping monocUne the limiting 

 scarp of which forms the eastern boundary of the Abert Lake Basin. This monocline 

 is limited on the east by the scarp of a second monocline of precisely similar nature, 

 and between the two scarps lies the Warner Valley. As usual, the deepest depression 

 Ues immediately under the scarp, being accentuated in this case by a minor parallel 

 faulting to the west of the axis of the depression. The depression is a long narrow 

 valley between a high steep scarp to the east, and to the west a much lower scarp 

 from the crest of which rises the gentle monocHnal slope before mentioned. To the 

 north and northwest the valley rises into a rolling plateau like those already described, 

 and across which passes the inconspicuous divide between it and the Harney Basin. 

 At the south the basin is limited by a zone of cross uplift and irregular faulting, 

 beyond which lies the Surprise Valley. 



The Warner Valley is entirely surrounded by high divides and seems to have been 

 always so inclosed. The surrounding mountains are furrowed by a series of lake 

 terraces of usual character, the highest of which is (by aneroid) a little over 200 feet 

 above the present lake. Several streams descend the gentle slope of the westward 

 monocline and reach the valley proper through narrow canyons cut in the basalt of 

 the low western scarp. During the lake period nearly all of these streams built 

 typical deltas, the remnants of which may still be seen. (PI. IV, fig. 1.) 



The present floor of the valley is a flat clay plain, probably once a playa, but now 

 diversified by considerable vegetation and by occasional dune areas .or wind-scoured 

 hollows. Shallow depressions hold two main lakes and several smaller ones, the 

 whole being known as the \\'arner Lakes. All of the lakes are either fresh or merely 

 brackish, but at the southeast corner of the northern or Upper Lake is a small pond 

 containing a nearly saturated solution of sodium chloride. Its salt is believed to be 

 derived from seepage. The separation of the Warner Lakes is very recent. They 

 are still variable in size and are reported to have been considerably larger about forty 

 years ago. 



