THE LOWEE ANCIENT VALLEY. 269 



This I do not think is compatible with the gentle curve made by the 

 bottom of the old channel. The intervolcanic erosion cut sharp, strep 

 canyons like those of to-day. The deepest "gutters"* in the Smarts- 

 ville channel might perhaps have been carved by it and it probably 

 swept away earlier accumulations of "white" or quartz gravel. From 

 Smartsville to French Corral there is only one wav which the Neocene 

 river could have followed, that of the present river canyon ; any other 

 way would necessitate extremely improbable and sudden changes of 

 grade. A scattered line of small deposits indicates that in all probability 

 the old river, near the mouth of Deer creek, received a tributary of which 

 one branch came from Nevada City and the other from Grass valley. 



Grades : 



Lowest point — Sicards Hat, 3-] miles, ('»<> feet per mile (?). 



Sicards flat — Timbuctoo, If miles, 100 feet per mile. 



Timbuctoo — Mooney flat,3 miles, 113 feet per milel Smartsville channel ). 



Mooiiey flat— French Corral, 1" miles, 7* feet per mile. 



The Nevada City and Grass Valley Channels. — In spite of the extensive 

 erosion west of Nevada City and Grass Valley there is pretty good evi- 

 dence that the channels of these places formed the old equivalents of 

 the present Deer creek and connected with the main Vuha river a short 

 distance above .Mooney Hat, three miles above Smartsville. The Nevada 

 City channel evidently headed a few miles east-northeast of that city in 

 the Harmony ridge, and is exposed in the East Harmony and Wesl 

 Harmony drift mines ;f it runs westward with a steep grade, and, curving 

 southward, emerges east of the Sugarloaf, in the old Manzanita diggings, 

 and thence passes on to the hydraulic mines northwest of the city 

 (American hill). From here on it is largely eroded away. .The large 

 amount of gravel in the lower part of this channel is remarkable. The 

 low divide toward the main river eastward formed a gateway through 

 which some of the rhyolitic tuffs poured down toward Nevada City. 



Grades : 



Manzanita — West Harmony, about 76 feet to the mile. 



West Harmony — Harmony, about 190 feet to the mile. 



The Grass Valley channel is somewhat different in having a compar- 

 atively small amount of gravel, it is covered with tuffs and volcanic 

 sands, above which, as usual, lies thecompact tuffaceous andesitic breccia. 

 It is separated from the Nevada City channel by a four-hundred feet 

 high bed-rock ridge, culminating in Banner hill. The first point where 



♦ "Auriferous Gravels," p. ;;s0. 



•(-These mines have been developed since Mr Pettee's visit to the place. 



