LAKES BOXXEVILLE AND LAHONTAN. 109 



volume is full and definite. He distinguishes as especially important two 

 great " fresh- water lakes which occupied depressed portions of the interior 

 drainage, — lakes whose former limits are indicated by singularly well-pre- 

 served terrace-lines traced around the ancient shores." For the eastern one 

 of these former lakes Mr. Gilbert's name has been adopted by the Fortieth 

 Parallel Survey; the other is called by Mr. King Lake Lahontan.* The first 

 of these, Lalve Bonneville, extended from about the parallel of 42^ southward 

 to 37' 30', the meridian of 113" representing nearly the middle of the lake. 

 The extreme width was in latitude about 40° 21', where the east and west 

 extent was 180 miles; from north to south it had a stretch of about 300 

 miles. The present level of Great Salt Lake is nearly 4,250 feet above the 

 sea ; that of Lake Bonneville was about 940 feet higher, making the altitude 

 of its ancient water surface at the time of the greatest extension of the lake 

 not far from 5,200 feet. Below the upper shore-line is a series of successively 

 lower terraces indicating a gradual recession of the waters down to the pres- 

 ent level. The former outlet was to the north, into the valley of Snake 

 River, as first suggested by Mr. F. H. Bradley, and afterwards proved by 

 Messrs. Peale and Gannett of the Hayden Survey. There were some north 

 and south trending islands, the tops of the present mountain ranges of the 

 region, in the lake at the time of its greatest development ; but the area of 

 water in Lake Bonneville was on the whole much less irregular than that of 

 Lake Lahontan. 



This last-named body of water, as defined bj' the explorations of the For- 

 tieth Parallel Survey, extended from 41"^ 30' southward to about the same 

 latitude as the southern waters of Lake Bonneville (37' 30'). The altitude 

 of the western lake was 4,388 feet, or about 800 feet lower than that of the 

 eastern one, and its area was also somewhat less. Lake Lahontan included 

 within its limits the present Walker's, Carson, Humboldt, Winnemucca, and 

 Pyramid lakes. The united area of these is about equal to half the present 

 lake surfixce of the basin of Bonneville. The outline of Lake Lahontan was 

 extremely irregular. Indeed, but little is known of its southern continuation, 

 and its limits in that direction could only be roughly made out.f It appears 



* A map showing the position and area of these two ancient lakes, and of sundry other smaller ones, lying be- 

 tween these, is given in Mr. King's yoliime. The data for this map were in part derived from the work of the 

 Wheeler Survey. 



t ChieHy from the barometric observations of Messrs. Gabb and Wilson, who were sent by the present writer to 

 explore the southwestern corner of N'evada in 1S67. 



