38 BULLETIN 54, U. S. DEPARTMENT OF AGRICULTURE. 
THE LEE CANYON BASIN. 
The Lee Canyon Basin is of very recent origin, occupying the northwestern end of 
the Las Vegas Valley, being separated from the main drainage of that valley by a 
divide less than 15 feet high. It was once the channel of the drainage of the Pint- 
water and Indian Spring Basins, as above noted. Because of its recency the basin 
has no importance to the present inquiry. Its area is 300 square miles. 
THE SHEEP RANGE BASIN. 
The Sheep Range Basin lies between the Sheep and Desert Ranges and east of the 
Pintwater Basin. Its northern third has never been mapped and is almost unknown. 
It may have drained into the Pintwater or directly into the Colorado drainage, or it 
may have been always inclosed. In any case, its small area of less than 300 square 
miles renders it unimportant. 
THE SPRING VALLEY BASIN. 
The Spring Valley is a trough valley of regular and normal type lying east of the 
southern part of the Steptoe Valley (see p. 20) and parallel thereto. Its northern end 
has never been mapped accurately and has not been visited by the writer. It is con- 
sidered probable that the valley once drained either northward into the Goshute 
Basin or northwestward into the basin of the Great Salt Lake, but it can not be said 
definitely that this is the case. The area of the basin is about 1,550 square miles, this 
area being somewhat approximate, owing to uncertainty as to the position and nature 
of the northern boundary. 
THE DESERT VALLEY DRY LAKES. 
In the Desert Valley, southwest of the town of Pioche, Nevy., is a group of small 
playas or ‘‘dry lakes.’’ These playas and the trough in which they lie were very 
recently tributary to the Colorado River drainage and are now cut off therefrom only 
by low alluvial divides. Neither they nor their basin has any importance from the 
present point of view. 
THE GANNETT BASIN. 
Near the station of Gannett, east of Las Vegas, on the San Pedro, Los Angeles & Salt 
Lake Railway, a former tributary of Muddy Creek has been dammed by alluvium 
with the formation of a small and shallow basin of very recent origin. Its drainage 
area is less than 150 square miles and both this small size and its recent origin render 
it of no importance. 
THE OPAL MOUNTAIN BASIN. 
The Opal Mountain Basin lies in an isolated trough between the McCollough Range 
and the Opal or Eldorado Range in the extreme southern corner of Nevada. It 
appears to be mainly structural and those divides which are superficially alluvial 
are high and probably ancient. The writer is inclined to regard the basin as pre- 
Lahontan, but has never visited it and can not advance a decided opinion. If over- 
flow ever did occur it was unquestionably into the Colorado River. The area of the 
basin is 580 square miles. It contains a playa of unknown area and character. 
THE TROUGH VALLEYS OF CALIFORNIA AND THE MOJAVE DESERT. 
South of the Lahontan Basin, the western boundary of the Great 
Basin is still the crest of the Sierra Nevada, which continues to run 
nearly north and south until just north of the thirty-fifth parallel, 
where the Sierras bend slightly westward to form the lower and more 
diffuse Tehachapi Mountains. These merge to the south into another 
