Hershey.i The River Terraces of the Orleans Basin . 



447 



rock floor under sand, but there are traces of an outer rim at 

 about ten feet above low-water mark. Over this the bank dis- 

 plays moderately fine river gravel fifteen feet thick, and above 

 this a bed of dark brown, non-pebbly sandy silt twenty-five feet 

 thick. Its surface at fifty feet above the river is the surface 

 of the terrace. 



The Modem Canon. — In the Upper Basin, the Klamath River 

 lias an estimated average widtb at ordinary stages of 300 feet, 

 but the Modern canon is mostly from 500 to 800 feet wide. The 

 river is building and rebuilding bars on the inner sides of the 

 curves. There is no flood-plain properly so called, except at a 

 very few places where it has recently piled sand and fine gravel 

 over the ordinary coarse gravel bars. At high water the canon 

 is flooded from wall to wall. At low water the stream winds 

 about in a manner suggesting overloading, but I think this is 

 due largely to the abnormal amount of material thrown into the 

 river during the past half century by the placer miners. In 

 fact, this disturbance of the natural conditions makes it inad- 

 visible to use the Modern river deposits as a basis for com- 

 parison. 



The present river channel opposite Orleans is probably 400 

 to 500 feet wide. Below the village the channel widens to from 

 one-fifth to one-third of a mile. At high water this is flooded 

 from side to side, but at low water the river flows through it 

 in a shallow channel from 100 to 150 yards wide, bordered by 

 bare gravel bars which rise to a maximum of ten or twelve feet 

 above the stream. This is one of the few places where the 

 Klamath Valley widens sufficiently to admit of the formation 

 of extensive Modern gravel bars. In the Lower Basin the 

 Modern canon is comparable with that in the Upper Basin. 



CHARACTERISTICS AND DIFFERENCES OF TERRACES. 



The three highest terraces, namely, the 850-foot, the 675-foot, 

 and the 475-foot terrace, have almost identical characters, and 

 may be considered together under the designation of the Upper 

 Group. The channel gravels of this group are relatively fine 

 and usually thin. The reddish brown sandy silts over the gravel 

 beds are flood-plain deposits built by the river during periods 

 of high water. They are unusually thick. The main tributary 



