28 BULLETIN 51, V. S. DEPAKTMENT OF AGEICULTUEE. 



and transient lake and that tlie basin was freely drained during the main Laliontan 

 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 tliat it previously drained into the Catlow Valley, but the eAidence 

 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 belieA'ed to have been tributary 

 to it, making a total of about 2.000 square miles. The remainder of the s^Ticline, 

 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 A'alley is a north-aud-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 tliis 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 A'alley 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 A-alley rises rather suddenly 

 to the highlands nmning east from Mount Bidwell and which separate it from the 

 Warner Valley. The structureof these highlands is also unknown. Southward and 

 eastward the valley rises more gradually to a relatively imdistiirbed lava plateau, 

 the features of which are diie 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 L^pper Lake sometimes evaporates entirely to drjiiess. 

 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 allu^•ial di^^de. A 

 series of old strands of usual character surround the whole valley and indicate pre"vious 

 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 BonneAdlle. Lake Annie, north 

 of Fort Bidwell, lies behind a wave bar of this kind built across the mouth of a narrow 

 canyon wliich was an estuarj^ of the ancient lake. 



On the crest of the northern di^dde, 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 tributarj^ 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 tributarj^ to the Surprise. If the area of this be included the total becomes 

 2,350 square miles. 



