494 PROCEEDINGS OF THE ALBANY MEETING 



SIERRA MADRE NEAR PASADENA 

 BY E. W. CLAYPOLE' 



\^Ahstract'\ 



The paper opened with an expression of the surprise with which geologists who 

 have worked principall}' in the east witness the enormous development and the 

 excessive diastrophism exhihited by Tertiary and even by very late Tertiary strata 

 in the west, and these characters are as well seen in California as in any other 

 western state. The whole Tertiary period has apparently been signalized by thick 

 accumulation, with alternate elevation and depression. Not less has its passage 

 been characterized by volcanic outbursts of intense energy and by quiet outflows 

 of lava almost unequaled in massiveness and extent. 



Two great mountain ranges diverging in the north and meeting again in Kern 

 county inclose between them the San Joaquin valley. This southern meeting 

 forms one of the great natural features of the State — the Tehachapi divide. 



Speaking now only for the southern part of the state, there seems ample ground 

 for the belief that these ranges have existed from at least Cretaceous, if not from 

 earlier .Mesozoic, time. It is not otherwise easy to find a source for the enormous 

 Pliocene, Miocene, and Eocene accumulations of the Pacific margin so far from 

 the Sierra Nevada. 



Thick gneissic strata of two types, and standing nearly vertical, compose the 

 range of the Sierra Madre near Pasadena. That to the south contains a large pro- 

 portion of hornblende, weathers rapidly and deeply, and is consequently eroded 

 with comparative facility. That to the north is largely feldspathic, contains 

 little hornblende, and of it consist the white crags that stand out so boldly on the 

 upper slopes. The former of these masses cannot be less than 2,000 to 3,000 feet 

 thick, but it <loes not rise in the mountain to a greater height than 8,r»00 feet. 



Of the wreckage from these two gneissic masses, the material tilling the valley 

 of Pasadena is composed. From great boulders near the foot of the Sierra it grad- 

 ually diminishes till it becomes, in many places, a fine gravel, and at last a fine 

 silt. This last composes tlie adobe land around Los Angeles, and also the many 

 sheets of the same material which lie in the gravel, and are the holding ground of 

 the water supply. This has been so largely exploited during the two late dry 

 seasons that the work has resulted in restoring confidence in the water resources 

 of the valley, of which some had become rather doubtful. 



The highly aluminous nature of many of these beds indicates a very extensive 

 decay or kaolinization of the gneisses of the Sierra and, together with the diluvial 

 arrangement of the Pleistocene wash in the valley, rather indicates a long contin- 

 uance of the present climatic conditions than a past of greater and stieadier rainfall. 



The multiplication of wells has not yet shown any effect in lowering the water- 

 level, unless perhaps in a few cases, and this result is the more surprising and 

 gratifying because it comes after two dry seasons, in which only 11 inches of rain 

 have fallen. Already this year a greater total has been received than the above, 

 though the wet period has scarcely begun. 



Wlien to this is added the storage of the rainwater in tanks and ponds and the 

 reforesting of the Sierras, wherever possible, it will be seen that the maintenance 

 of the water supply in the future is encouraging. 



