Mount aim of the South 233 



siderable area. East and west of The Pipes are flat-topped 

 summits, also flat-topped ridges occur on both sides of Antelope 

 Creek. All these flat surfaces are at about the same level as the 

 summit ridge between the high peaks San Gorgonio and San 

 Bernardino. The fact that these flat areas extend across eroded 

 surfaces of gneisses, schists and basalts as well as granite sug- 

 gests that these are remnants of an old peneplain, or worn-down 

 landscape. This ancient land surface existed before the San 

 Bernardino Range was uplifted. The difference in elevation 

 between these remnants of an old land surface and the broad 

 valley floors and meadows indicate the amount of the uplift. 

 The summit ridge between San Bernardino and San Gorgonio 

 mountains rises 4,000 to 4,800 feet above Big Meadows and the 

 floor of Bear Valley. This then represents the amount of up- 

 lift that occurred during the time that this vast erosion was 

 going on.* 



An Ancient Worndown Land Surface 



About eight miles north of the high ridge between San Gor- 

 gonio and San Bernardino mountains is an ancient land surface 

 (peneplain) having broad valleys and meadows, and hills with 

 rounded profiles. The general elevation is around 7,000 feet 

 above sea level. The most important valley is Bear Valley, 

 extending 12 miles in an east-west direction. Bear Lake, five 

 or six miles in length, lies in the lower part of the basin and 

 Baldwin Lake in the upper part of the basin. The basin is 

 drained by Bear Creek to Santa Ana River through a precipi- 

 tous gorge. The region of Bear Valley and Holcomb Valley 

 to the north is in a stage of topographic "old age." Streams of 

 low gradient flow sluggishly through the meadows, but plunge 

 down steep canyons in their lower courses as they descend from 

 the uplifted land. 



North of Bear Valley about seven miles the surface breaks 

 off by a precipitous declivity to the Mojave Desert. East and 



* F. E. Vaughan, Univ. of Calif. (See Appendix.) 



