The Valley of the South 269 



Blue Hill because a distinctively blue crystalline limestone oc- 

 curs in it. In the other, called Chino Hill, the limestone is a 

 pure white marble. Limestone occurs as one of the sedimen- 

 tary formations in the San Bernardino Mountains. The San 

 Bernardino Mountains have been far uplifted above the River- 

 side plain and all the San Bernardino Valley. Limestone occurs 

 in Sky Blue and Chino Hills. Is is reported to occur also in 

 other hills a few miles west, and probably in Slover Mountain 

 near Colton. Are these limestone deposits now metamor- 

 phosed out of all resemblance to their former character 

 remnants of a widespread formation that formerly existed over 

 the whole valley, a part of the ancient roof rocks that were up- 

 lifted by the intrusion of the molten granite magma, and now 

 remain as the caps of worn-down mountains and hills? It 

 would seem so. 



Are the Limestone Hills Young 

 or Old? 



Are these limestone-capped hills then old or young? At 

 their bases is the very old granitic rock. But the peaks, like 

 Mount Rubidoux, have just been formed by erosion. They 

 are in process of "forming" now, that is, they are being worn 

 down all the time. They are being "made" into peaks by wind 

 and weather at this very time, every day. Are the hills then 

 old, or are they young just being formed? 



The blue crystalline limestone, blue calcite, that occurs in 

 Sky Blue Hill, is a somewhat rare mineral. It occurs elsewhere 

 in California. (It has been reported from mountains in the 

 Mojave Desert.) The cause of the blue color is not known. 

 There are also pale pink and green limestones in the Sky Blue 

 Hill. The mineral occurs as crystals of calcite (calcium car- 

 bonate) in seams, bands, and patches mixed with other meta- 

 morphic minerals. The Sky Blue Hill limestone capping was 

 subjected to later metamorphic action by intrusion of highly 

 heated igneous rock and the action of mineralized solutions. 



