28 BULLETIN 54, U. S. DEPARTMENT OF AGRICULTURE. 
and transient lake and that the basin was freely drained during the main Lahontan 
period. This could be determined only by extensive detailed study. Nothing at 
all is known concerning the Quaternary history of Guano Lake. The writer inclines 
to the opinion that it previously drained into the Catlow Valley, but the evidence 
favoring such a conclusion is too insignificant to warrant its acceptance. 
The present drainage of the Catlow Valley aggregates perhaps 1,000 square miles. 
During the Lahontan period about as much again is believed to have been tributary. 
to it, making a total of about 2,000 square miles. The remainder of the syncline, 
including the Guano Lake Basin, has an area of approximately 1,000 square miles, 
which may or may not have been tributary to the latter. 
THE SURPRISE BASIN. 
The Surprise Valley is a north-and-south trough lying immediately south of the 
Warner trough and appearing at first sight to be a continuation of it. Closer examin- 
ation, however, casts considerable doubt upon this conclusion. The structure of the 
Surprise trough is much more complex and has never been studied in detail. The 
deepest depression and highest range are here on the western side of the valley, and 
if the structure is monoclinal the inclination is reversed from that exhibited in the 
Warner. From a cursory examination of the valley and the range which borders it 
on the west, the writer is inclined to the opinion that folding has had almost as much ~ 
to do with the structure as has faulting and that the appearance of analogy to the 
Warner Valley is appearance only. To the north the valley rises rather suddenly 
to the highlands running east from Mount Bidwell and which separate it from the 
Warner Valley. The structure of these highlands is also unknown. Southward and 
eastward the valley rises more gradually to a relatively undisturbed lava plateau, 
the features of which are due to folding and erosion much more than to faulting. The 
low and featureless range which separates the Surprise Valley from Long Valley on 
the east suggests a gentle anticline of north-south axis, but this is by no means certain. 
The present floor of the valley is very similar to that of the Warner Valley, being 
essentially a great playa, in shallow depressions of which stand the Upper, Middle, 
and Lower Surprise Lakes. This plain is somewhat less diversified than that of the 
Warner and its playa character is more apparent. The lakes are very variable and it 
is reported that the northern or Upper Lake sometimes evaporates entirely to dryness. 
The Lower or southernmost lake is connected with the Middle Lake by a narrow 
slough, the latter being separated from the Upper Lake by a low alluvial divide. A 
series of old strands of usual character surround the whole valley and indicate previous 
occupation by a single great lake which stood about 350 feet above the present floor 
and was permanently without outlet. This lake has left wave bars, terraces, etc., 
which rival in completeness those of Lahontan and Bonneville. Lake Annie, north 
of Fort Bidwell, lies behind a wave bar of this kind built across the mouth of a narrow. 
canyon which was an estuary of the ancient lake. 
On the crest of the northern divide, east of Mount Bidwell, lies the small basin of 
Cowhead Lake, once a tributary of the Surprise, but now cut off by desiccation. 
New Year Lake, near the crest of the eastern divide, is of similar character. South of 
the valley the large basin of Duck Flat, also at one time a tributary and later filled by 
an arm of the ancient lake, has been cut off by a low and recent alluvial divide to form 
an inclosed basin. 
The present tributaries of the valley include only a number of short mountain 
streams, mostly intermittent in character. The area now tributary to the valley is 
about 900 square miles. With Duck Flat and the basin of Cowhead and New Year 
Lakes the area is 1,580 square miles. It is possible that Long Valley, to the east, was 
also once tributary to the Surprise. If the area of this be included the total becomes 
2,350 square miles, 
