RIVER TERRACES AND GLACIAL SERIES 435 



several beautiful remnants of the middle terrace (Channel D), 

 half way down to the river. There is no room for the lower 

 terrace. Above Channel C there seem to be several remnants of 

 a level 30 or 40 feet above it (Channel B). Still higher there 

 is a little channel about 30 feet wide, with a distinct outer rim 

 of bed- rock, a few bowlders and a little gravel in the channel and 

 this overlaid by about 20 feet of red, indistinctly stratified, 

 rather subangular local debris. This may occur nearly 175 feet 

 above the river and probably approximately represents Channel 

 A. Far below it is the main upper terrace. 



Just below Big Bend Creek, the covering of the regular river 

 gravel in the main upper terrace by brown, not red, distinctly 

 stratified and partly water-worn hornblende schist pebbles and 

 subangular debris, as in Cooper's mine, becomes quite apparent. 

 This is the downstream edge of the torrent fan of Crosby Creek, 

 elsewhere discussed, and it is here 20 to 40 feet thick. It buries 

 two channels. At 65 feet above the river we have the floor of 

 Channel C, which from here upstream becomes the main or best 

 developed upper channel. We know that it is Channel C because 

 this is one of the four points just mentioned, and we can see that 

 it absolutely corresponds to the channel which, farther down 

 stream, stands at 75 feet above the river. The canyon is getting 

 shallower. Channel D occurs on the opposite (south) side of 

 the river at only 20 feet above the stream. 



Channel C contains some large bowlders of Courtney granite 

 and the regular river deposit is covered by about 40 feet of the 

 Crosby Creek alluvium. Just back of it we have at 80 feet 

 above the river, Channel B, which contains few large bowlders 

 and is covered by a less thickness of the Crosby Creek alluvium. 

 It is quite evident that the mass of local debris which came with 

 a rush of water down Crosby Gulch and was distributed down 

 the valley and stratified by the river, rests on nothing lower than 

 Channel C of the Summerville basin. It is of the same age as 

 the completion of this channel and it is the equivalent of the 

 local debris which nearly everywhere seems to form the surface 

 deposit of the main upper terrace of the Summerville basin and 

 gives it its sloping surface. Its relation to Channel B is simply 



