8 University of California Puhlications i)i Botany [Vol.9 



A feature of high mountain rocks which has a most important 

 bearing- on their disintegration, and also on the vegetation growing 

 on them, is the jointage. Over wide areas all the rocks will be found 

 jointed, the slates and schists more minutely than the granites. In 

 other places the granite appears perfectly massive. The joint planes 

 sometimes appear to be in systems, coinciding in direction and angle 

 over several square miles; in other places no such regularity can be 

 made out. On the high summits and on the walls of cirques the rock 

 is apt to be jointed in three planes, the whole being divided up into 

 more or less cubical blocks, which are often freely movable on the 

 exposed peaks and aretes. Becker^^ noted in the region north of 

 Yosemite, where horizontal jointage predominates, that the granite 

 mountains appeared somewhat terraced ; in his opinion the fissures are 

 really minute faults. In the Yosemite region Matthes^" finds distinct 

 areas of massive and jointed granites. On the south slope of Mt. 

 Raymond, Madera County, the coarse-grained granodiorite is so regu- 

 larly jointed that the blocks appear as if squared for rough masonry. 

 On Kuna Crest, above Tuolumne Meadows, in the Yosemite district, 

 the granodiorite is also regularly jointed. (See plates 1 and 3, show- 

 ing jointage.) 



TOPOGRAPHY* 



Wliile the present surface of the boreal region of the Sierra is 

 highly diversified, in this complexity of topographic form are certain 

 indications of a general symmetry. Viewed from a distance the in- 

 equalities appear to blend into fairly regular contours ; plate 1 shows 

 the summit region of the southern Sierra. This feature of the high 

 Sierran topography has been studied in detail by Lawson® for the 

 southern Sierra of Tulare County, and by Lindgren^^ and Reid^^ for 

 the Tahoe district ; the results of their investigations indicate an old 

 erosion surface. Above this surface the highest summits of the exist- 

 ing range projected as a range of low mountains. With the pro- 

 gressive elevation of the region along the eastern margin, the result 

 of movement along the fault lines differentiating the Sierra from the 



* The following maps ("quadrangles"), issued by the United States Geo- 

 logical Survey, cover the region considered in this paper. The sequence is from 

 north to south. 1, Lassen Peak; 2, Honey Lake; 3, Bidwell Bar; 4, Downieville ; 

 5, Sierraville; 6, Colfax; 7, Truckee; 8, Pyramid Peak; 9, Carson; 10, Marklee- 

 ville; 11, Dardanelles; 12, Bridgeport; 13, Yosemite; 14, Mt. Lyell; 15, Mariposa; 

 16, Mt. Morrison; 17, Kaiser; 18, Mt. Goddard; 19, Tehipite; 20, Bishop; 21, 

 Mt. Whitney; 22, Kaweah; 23, Olancha. 



