268 Adventures in Scenery 



the adjacent higher lands were deposited. These fine sediments 

 are the clays that are now the source of the material from which 

 the terra cotta works at Alberhill have been developed. The 

 clays have been eroded into hills. Are these hills old or young? 



Mount Rubidoux stands up near Riverside as a bold rugged 

 granite monument. It is apparently a part of the granite 

 bedrock that underlies the San Bernardino Valley and the 

 hill-dotted plain to the south (Ferris Plain) . Are Mount Rubi- 

 doux and other granite monadnocks that stand above the inter- 

 vening valleys old or are they young? West of Riverside, near 

 Corona, a very old granitic rock, technically known as grano- 

 diorite, is quarried from an old worn-down mountain. The 

 granite was a molten magma in (probably) Jurassic time; a 

 molten liquid mass that was forced up as a batholith under the 

 rocks that originally existed here. The overlying roof rocks 

 have been removed by erosion during long ages, and the moun- 

 tain stump which is now being quarried, and other granitic 

 peaks and ridges, are remnants of the once molten mass that 

 long ago cooled and crystallized under the overlying roof of 

 ancient sedimentary rocks. Are these crags and peaks then old 

 or young? They are remnants that are left after a long time 

 of erosion. As they stand they represent a late chapter in the 

 long story of uplift and erosion. As crags, peaks and ridges 

 they are young. As rocks they are very old. 



A few miles west of Riverside (at Crestmore) are some hills 

 in which limestones occur highly metamorphosed by heat and 

 chemical activity related to the molten magma that has been 

 spoken of. The base of the hills the bed-rock underneath 

 is the rock technically called granodiorite, which is the "gran- 

 ite" underlying the mountains. The limestone is metamor- 

 phosed to a highly crystalline marble. No fossil remains have 

 been discovered, and the age of the limestone is therefore not 

 known. If fossil remains were once there, entombed in the 

 sediments, they have been utterly destroyed as to their original 

 forms by the extreme metamorphism. One hill is called Sky 



