CHUECHILL VALLEY. 137 



EXPOSURES IN THE CANOX OF THE CARSON RIVEK. 



During the highest stages of Lake Lahontan its waters extended up 

 the Carson River Valley as far as Dayton, and occupied it long enough to 

 allow large quantities of lacustral beds to accumulate. When the lake 

 evaporated and the river regained its ancient channel, these beds were deeply 

 dissected by erosion. The remnants of Lahontan sediments to be seen in 

 the valley belong mostly to the upper lacustral clays, but in places they 

 were observed to rest on gravel deposits. The sections obtained, however, 

 were imperfect and far less satisfactory and instructive than those described 

 in the preceding pages. The lacustral beds exposed along the banks of the 

 Carson, and flooring Churchill Valley, are fine, light-colored marly-clays, 

 similar in all respects to the corresponding beds observed at many localities 

 throughout the Lahontan basin. Interstratified with these sediments is a 

 deposit of dendritic tufa, sometimes 3 or 4 feet in thickness, which is well 

 exposed in the narrow channel connecting Churchill Valley with the Cai'- 

 son Desert. This deposit corresponds both in structure and position to the 

 interstratified tufa-layer observed in the Humboldt and Truckee canons. 



So far as known, the lacustral beds observed along the Carson River 

 are undisturbed by post-Lahontan movement, and have nowhere been dis- 

 sected sufficiently deep to lay open the sediments accumulated during the 

 first rise of the lake. 



The Carson River rises on the eastern slope of the Sierra Nevada and 

 flows northward through Carson and Eagle valleys, which are in reality a 

 single basin, and enters a deep and all but impassable canon, through which 

 it flows with a rapid descent as far as Dayton. It then enters a valley 2 or 

 3 miles broad — once an arm of Lake Lahontan — which contracts again to 

 a narrow calion at its southern end. In the course of a few miles this canon 

 again expands and forms Churchill Valley, which in its turn connects with 

 the Carson Desert through a narrow channel now occupied by the Carson 

 River. The contractions in the lower portion of the river channel are prob- 

 ably due in a great measure to erosion, but are less plainly stream-carved 

 channels than the deep gorge above Dayton. Since Lake Lahontan during 

 its highest stages occupied the valley as far as Dayton, we are safe in con- 



