TOPOGRAPHIC FEATUEES OF THE DESERT BASINS. 11 



This classification, while setting out to be both genetic and geo- 

 graphic, has ended by being scarcely more than arbitrary, but this 

 seems not to be remedied, and it is hoped that the index and the key 

 map will help to cover the lack of a more logical arrangement. Each 

 basin or group of basins has been given a name by which it is known 

 throughout the report and which is, wherever possible, the name by 

 which it is known to residents of the neighborhood or in former 

 geologic studies. These names are given on the accompanying 

 map, in the index, and in the synoptic list of Table I (p. 60) and will 

 enable the ready location of information concerning any basin or 

 region. 



THE LAHONTAN BASIN AND ITS TRIBUTARIES. 



At the present time the Lahontan Basin contains internal divi- 

 sions, structural and alluvial, dividing it into a number of separate 

 basins of which the major are the Black Rock Basin, the Humboldt- 

 Carson Basin, the Truckee or Pyramid Lake Basin, and the Walker 

 Basin. The studies of Russell ^ have shown that the water of Lake 

 Lahontan rose sufficiently to unite all of these basins into one water 

 body. At the highest stages of the lake the present Humboldt-Car- 

 son Basin was connected with the Walker through the pass south of 

 old Fort Churchill, with the Truckee through the Ragtown Pass 

 and the pass at Wadsworth, and with the Black Rock through the 

 pass north of Humboldt Station on the Southern Pacific Railway, 

 the latter basin being also connected with the Truckee at the north 

 end of the present Pyramid Lake. Both the Black Rock and 

 the Truckee Basins were connected with the smaller Honey Lake 

 Basin through passes at the northwest corner of the present Pyramid 

 Lake. At this time the drainage area of the Humboldt River was 

 much greater than at present, a large part of it having since been 

 cut off by alluvial damming. The areas tributary to the Truckee 

 and Walker Rivers were also slightly larger than now. The Carson 

 was practically the same. 



As the waters of the lake went down the first divide to appear 

 was probably that between the Humboldt-Carson and the Allan 

 Springs Basin, a small tributary to the south. Next the Walker 

 became a separate basin, though perhaps continuing to overflow 

 into the Humboldt-Carson. At about the same stage the direct 

 connection between the Humboldt-Carson and the Black Rock 

 was broken, though there still remained the indirect connection 

 through the Truckee. A hundred feet additional lowering saw the 

 appearance of the divide at Wadsworth between the Humboldt- 

 Carson and the Truckee and the separation of the original lake into 

 three water bodies — the Black Rock, Honey Lake, and Truckee 



1 U. S. Geological Survey, Monog. XI (18S5). 



