470 



University of California . 



[Vol. 3. 



I will arbitrarily reduce the assigned age of the highest terrace 

 to 250,000 years. 



The portion of the Sierran Canon above the 850-foot terrace 

 is more than three times as deep as that below, several times as 

 wide, and has characteristics indicating a much greater age. 

 It is undoubtedly conservative to assign it a period of erosion 

 not more than three times as great as the age of the highest 

 terrace, or 750,000 years. This yields a total age for the Sierran 

 Canon of 1,000,000 years, and that figure also represents my 

 idea of the probable length of the Quaternary Era. 



The Sherwood Valley has the appearance of being at least 

 five times as old as the Sierran Canon, or 5,000,000 years. The 

 geologists who are working in the Pacific Coast country are 

 inclined to assign much longer periods of duration to the Plio- 

 cene and Pleistocene than do those whose field lies in the Eastern 

 States. Recently Dr. A. C. Lawson has given* as a possible 

 duration for Quaternary time, 2,751,000 years. However, he 

 includes in the Quaternary the period of erosion of a series of 

 "High Valleys" of the Upper Kern Basin, which valleys appear 

 to me to be the correlatives of the Sherwood Valleys of the 

 Klamath region. My figure corresponding to his given above is 

 6, 000,000 years. 



For several years I have entertained the idea that the Sierran 

 Canons have been in process of erosion for at least a million 

 years. I have been diligently searching for evidence of rapid 

 erosion, and in general have secured only negative results. I 

 will not deny that in places the streams are actively under- 

 mining steep slopes and causing landslides, but the total amount 

 of material thus removed in a century is very small. Along the 

 South Fork of Salmon River there has been little change in the 

 positions of large boulders in half a century. Fir trees 300 

 years old frequently stand on low Modern flood-plains in the 

 small gulches. On the steep mountain sides, although the sur- 

 face debris is very loose and apparently in movement down the 

 slopes, there can be little lowering of the surface in a period 

 of 100 years, as may be determined by an observation of the 

 timber. The debris accumulates against the upper sides of 



'"Bull. Dept. Geo!., Univ. Calif'., Vol. 3, No. 15, p. 3(58. 



