﻿174 J. LeConte — Elevation of the Sierra Nevada. 



nels, but rain-erosion still continued to widen the valleys and 

 cut down the divides. The river-system had therefore assumed 

 the form characteristic of old topography. Then came the lava 

 flood displacing the rivers, and the contemporaneous elevation 

 changing the base-level and enormously increasing the erosive 

 power of the rivers. These therefore without loss of time, 

 commenced cutting anew and in comparatively short time have 

 cut far lower than before. And because they have worked 

 rapidly and are still working, the canons are deep Y-shaped. 

 The Tertiary rivers were working during the whole Cretaceous 

 and Tertiary ; the present rivers only during the Quaternary and 

 present. The working time of the former was many times 

 greater than that of the latter ; and yet the present rivers have 

 cut much deeper. It is impossible to explain this except by 

 supposing a great rise, probably several thousands of feet with 

 increased slope of the range, at the end of the Tertiary. 



This Post-tertiary elevation of the Sierra extended far be- 

 yond the limits of the lava-flood. The lava-flood was a concom- 

 itant, possibly a result, not the cause of the elevation. In 

 Southern California beyond the limits of the lava-flood we 

 have equally convincing evidence of great elevation at this 

 time. Here the rivers were not displaced — they continued to 

 occupy the same places, but commenced to cut deeper at that 

 time. The evidence of this is found in the fact that remnants 

 of the old river-gravels are now found clinging high up on the 

 slopes of the present canon-sides. The relation of the old to 

 the new river beds in Southern California is shown in the ideal 

 section, fig. 7, in which the letters indicate the same as in pre- 

 vious figs. I first observed this during the summer of 1883 in 



Ideal section across a river bed in Southern California, r, Present river bed ; 

 r' r'\ old river bed. 



Lytle Creek Canon where the old gravels high up on the sides 

 of the present canon-walls have been worked for gold with in- 

 different success in several places. I visited and examined 

 them carefully. I have heard of a similar relation in other 

 places but have not examined them. There can be no doubt 

 therefore that the elevation extended the whole length of the 

 Sierra. The maximum was probably in the region of the 



