H. J. Biddle — Surface Geology of Southern Oregon. 481 



Upper, Middle, and Lower, Alkali Lake. During the summer 

 these lakes often dry up completely, leaving broad, level 

 stretches of fine-grained yellow mud. When visited by the 

 writer in September, 1887, the middle lake was quite dry, the 

 others nearly so. The water in the upper or northernmost 

 lake was found to be a strong saline and alkaline solution. It 

 contained about 45 grams of solids to the liter, mostly sodium 

 chloride. By digging into the mud near the center of the 

 middle lake the following section was obtained, beginning at 

 the surface : 4 feet of yellow fine-grained mud, 3 inches of fine 

 white volcanic dust, 3 feet of black mud smelling of hydrogen 

 sulphide. At the depth of seven feet the hole in the lake bed 

 filled with brine, which was found to contain about 38 grams 

 of salts to the liter — mostly sodium chloride, with some car^ 

 bonate and sulphate. This shows what has become of the salts 

 which must have accumulated during a long period in the 

 basin of the ancient lake. But a fraction of the total amount 

 exists in the shallow lakes of to-day; the greater portion must 

 be looked for in the brine saturating the mud beneath them to 

 an unknown depth. 



The existence of a stratum of volcanic dust .in this valley is 

 a fact of interest hitherto unreported. Similar strata occur 

 among the sediments of the ancient Lake Lahontan, as re- 

 ported by I. C. Russell.* That writer regards them as derived 

 from the craters about Mono Lake, Cal., and has observed such 

 material up to 200 miles from the supposed place of eruption. 

 The middle of Surprise Valley is about 250 miles from Mono 

 Lake, but less than half that distance from the volcanic region 

 of Mt. Shasta and Lassen's Peak. Further observations are 

 necessary to determine from which direction the volcanic dust 

 of Surprise Yalley was derived. There seems to be in this oc- 

 currence evidence of very recent volcanic activity. The time 

 in which a narrow lake, receiving annual supplies of sediment- 

 laden water and seolian dust, has deposited four feet of mud in 

 its bed, can hardly be very great. 



The region next to be considered lies on the border of the 

 Great Basin, and possesses the same topographical features as 

 the valleys previously mentioned ; but now belongs partly to 

 the hydrographical area of the Pacific. This is the region em- 

 braced in the valleys of Rhett Lake, and the Upper and Lower 

 Klamath lakes. It lies partly in Oregon, partly in California. 

 The whole may be regarded as one valley, formed by a compli- 

 cated system of faults, -with a nearly level floor on which the 

 lakes mentioned lie. Two of these lakes, the Upper and 

 Lower Klamath, discharge their waters by way of the Klamath 

 River into the Pacific, while Rhett Lake on the other hand 



* Lake Lahontan, p. 146. 



