326 University of California Publications in Geology L VoL - 13 



still having a pronounced relief with rounded forms (pi. 19). The 

 broad valleys had reached base-level before being uplifted. Crossing 

 over the ridge to the south into Santa Ana Canon a somewhat similar 

 situation obtains. Big Meadows at the head of the canon have the 

 same general appearance as the meadows in Bear and Holcomb valleys. 

 In Bear Valley there are remnants of an old surface above the present 

 floor ; as for example the plateau between Rathbone Creek and Erwin 

 Lake. Holcomb Valley is nearly surrounded by similar benches. Like- 

 wise around Big Meadows, particularly to the north and east and just 

 a little above them in general elevation, there are broad flats and flat- 

 topped ridges. In both cases the flats merge more or less into the hills, 

 but are rather sharply set above the meadows. However, some very 

 significant differences are to be noted. The surface of Big Meadows 

 is continuous with a great bench which extends several miles down the 

 canon, and on this bench there are several meadows. This was pre- 

 viously the floor of Santa Ana Canon, but it is now deeply incised by 

 the river, the new channel exposing about 500 feet of fanglomerate 

 (pi. 20A) , which shows that after the canon was first carved the climate 

 became less humid and the streams were unable to carry away their 

 burdens. This same change in humidity is recorded in Bear and Hol- 

 comb valleys, for the benches above the lakes and meadows are mostly 

 fanglomerate. Holcomb Valley is drained by Holcomb Creek, and 

 this cuts bedrock at the very edge of the valley, thus showing that the 

 filling of the valley cannot be very deep. Therefore the topography 

 must have been of the broad rolling type before the deposition of the 

 fanglomerate. But Santa Ana Canon was cut 1000 feet below Bear 

 Valley and had steep sides. The difference is further reflected in the 

 nature of the fanglomerate. In Santa Ana Canon boulders three to 

 six feet in diameter are common, while in Bear and Holcomb valleys 

 they are seldom greater than one foot. These valleys have broad level 

 floors ; into Bear Valley flows Rathbone Creek, a gentle graded stream, 

 and a similar creek from the region of Erwin Lake south of Baldwin 

 Lake. The old floor of Santa Ana Cailon differs in that it is not flat 

 but has a decided grade, being about 1500 feet lower at Seven Oaks 

 than around Big Meadows. In other words, the Bear Valley region 

 possesses some of the features of old age while Santa Ana Cailon rep- 

 resents late maturity. The following explanation of all of these 

 differences between the two regions seems plausible. 



In discussing the structure it will be shown that the mountain 

 mass has been uplifted between faults on the north and south sides. 



