222 SMITH AND CURTIS — CAMASLAND : A VALLEY REMNANT 



and capture of the Camasland drainage will doubtless continue, since the 

 greater thickness of the diabase sheet at the northern end where it is 

 crossed by Camas creek gives the pirate stream a decided advantage. 

 As Camasland is underlain by the sheet of resistant rock, it is a rela- 

 tively permanent land-form in consequence of the geologic structure, 

 and after the thin alluvial filling is more or less swept away through a 

 lower outlet to the south, it seems probable that Camasland will still 

 remain as a mesa — high above the surrounding country. 



By reason of its geologic structure, then, Camasland presents a fine 

 example of a valley remnant. So perfect is the preservation that even 

 so delicate a feature as the h 1 oodplain of fine alluvium has resisted erosion. 

 Such an exceptional and at the same time complete interruption of stream 

 processes causes Camasland to afford a strong contrast to the mature 

 topography of the surrounding region, where stream work has pro- 

 gressed further. The model figured in plate 20 thus illustrates two 

 stages in drainage history, and presents an example of past as well as 

 of present work by streams. 



