218 Adventures in Scenery 



Half Dome Formed by Exfoliation 

 of Granite 



The most imposing and most strangely shaped dome, and 

 one that will be certain to catch the eye and engross the atten- 

 tion of the observer standing on Glacier Point, is Half Dome, 

 which stands at the head of the Yosemite Valley on the divide 

 between Tenaya Canyon and the Little Yosemite. Rounded 

 on the south side and cut off sheer on the north side, it has the 

 appearance of a great dome that has been split in two and whose 

 other half has been destroyed. Measured parallel to its sheer 

 front it is nearly a mile long. The total height of the dome 

 above Tenaya Canyon is 4,770 feet. Viewed from Glacier 

 Point the tourist is almost bound to ask what has become of 

 the other half of Half Dome. Briefly answered it was never 

 there. Had there been another half of the dome consisting of 

 a gigantic monolith it would be still in existence to-day, for 

 neither the Tenaya Glacier nor the agents of erosion that shaped 

 the preglacial valley of Tenaya Creek could have demolished it. 

 It is generally recognized by geologists that the domes, which 

 form so conspicuous a feature of the Yosemite region, owe their 

 rounded forms to the exfoliation of massive granite, that is, the 

 casting off of successive curving shells or scales from their ex- 

 posed surfaces. The cause of exfoliation is not fully under- 

 stood. That the shells burst loose from the core of a dome 

 because of expansive stresses in the granite is clear from the 

 facts of observation, but how the stresses originate is not fully 

 known. In brief the probable cause is thought to be relief 

 from pressure experienced by the granite as the overlying masses 

 of rock are removed by erosion. The form of Half Dome, as 

 indeed of the many domes for which the Yosemite region is 

 famous, is due to the process of exfoliation. The curving back 

 of the dome is evidently a product of long-continued exfolia- 

 tion. Shells have been formed on it and have been dropped 

 from it in succession for millions of years. The straight sheer 

 front of Half Dome is by comparison a rather new feature, yet 



