42 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



reported to be impassable for horsemen for a number of days together dur- 

 ing the high -water stage. At this season its waters form a sliallow lake of 

 variable size, on Black Rock Desert, that is said, at times, to be 50 or GO 

 miles long by 20 broad. As the dry season advances, this playa lake 

 evaporates, leaving a vast mud-plain; the river at the same time shrinking 

 back 75 or 100 miles. During the highest stages of Lake Lahontan, Quinn 

 River had no existence, the greater part of its valley being occupied by an 

 arm of the lake. 



TRUCKEE RITER. 



The Truckee River has its source in the overflow of Lake Tahoe and 

 is of greater purity and subject to less fluctuation than any other stream 

 that enters the Lahontan basin. The lake which gives it birth is situated 

 at an elevation of 6,247 feet" amid the peaks of the Sierra Nevada; from 

 this reservoir the water descends with a fall of 2,466 feet,'* to Pyramid and 

 Wiimemucca lakes, where it is evaporated, leaving the lower lakes alkaline 

 and saline. The river is quite largely used for irrigation in the neighbor- 

 hood of Reno, and to a small extent between Reno and Wadsworth. A few 

 miles from Pyramid Lake a good-sized ditch has recently been constructed 

 for the irrigation of the lands of the Indian reservation. 



An analysis of the waters of Lake Tahoe, by Prof F. W. Clarke, which 

 may be considered as representing the normal condition of the Truckee 

 River, is given herewith: 



Constitueuts. 



Silica (SiOi) 



Magnesium (Mg) — 



Calcium (Ca) 



Sodium (Na) 



PotuBsium (K) 



Uhlorine (CI) 



Sulpburio acid (SO4) . 



CarlKHiic acid (CO3) l>y ditfereuco. 

 Total 



One liter of 

 water con- 

 tains, in 

 grammes — 



0. 0137 

 0. 0030 

 0. 0093 

 0. 0073 

 0. 0033 

 0. 0023 

 0.0054 



0. 0443 

 0. 0287 



0. 0730 



Per cent, in 

 total solids. 



18.77 

 4.11 

 12. 74 

 10.00 

 4.52 

 3.14 

 7.40 



00.68 

 39.32 



Constituents. 



Silica (SiOz) 



Magnesium carbonate (MgCos) 



Calcium carbou.ite (CaCoa) 



Sodium chlorido (NaCl) 



Potassium cbloridti (K("l) . 



Sodinm sulphate { NavSo4) 



Potassium sulphate (K2S04) .... 

 Sodium carbonate (NasCos) 



Total (99.04 per cent, accounted 

 for) 



Probable com- 

 bination (in 

 grammes per 

 liter). 



0. 0137 

 0. 0105 

 0. 0232 

 0. 0012 

 0. 0034 

 0. 0052 

 0. 0034 

 0.0117 



" Determined by Pacific Railroad surveys. 



"Elevation of Pyramid Lake, 3,781 feet. See postea, page 101. 



