Abstract Much of today will be spent in the plutons that are the principal host rocks of the western margin of the Tuolumne Intrusive Complex ( Fig. 3-1 ). These include the Sentinel and Yosemite Creek granodiorites (Kistler, 1973; Bateman, 1992) and the Yosemite Valley Intrusive Suite ( Bateman, 1992 ). The Sentinel and Yosemite Creek Granodiorites were tentatively included as part of the Tuolumne by Kistler and Fleck (1994) and Bateman (1992), but assignment of these plutons to the Tuolumne has been hampered by lack of detailed study. We and our students and colleagues have been mapping and conducting focused studies on the petrology, geochemistry, and structure of both plutons recently, but the results are presently only in theses and abstracts (Petsche, 2008; Fulmer and Kruijer, 2009; Bliekendaal, 2012; van der Linde, 2012; Johnson, 2013). Reasonably accessible exposures of these units can be seen along Highway 120 within Yosemite National Park

Abstract Since the days of John Muir, the striking granitic topography of Yosemite Valley, California, has been understood to have been sculpted by glaciers and presently modified by rockfall. Glacial erosion has provided remarkably clean and extensive exposures of granitic rocks on the vertical walls that provide insights into intrusive relations and rockfall susceptibility. However, it is only with recent remote sensing methods that these exposures have been studied in detail. El Capitan presents an unparalleled exposure of the interior of a granitic plutonic system at the point of interaction between multiple intrusive suites and two sets of mafic dike swarms. The distribution and orientation of these units affected El Capitan's extensive rockfall history, including a huge postglacial rock avalanche at 3.6 ka. This two-day field trip will explore these ideas and apply them to some of the other classic cliffs of Yosemite Valley such as Glacier Point and Half Dome. We will present a new map of El Capitan and discuss the intrusive relationships exposed on the face while visiting several rockfall deposits and some of the classic vistas of Yosemite Valley, including El Capitan Meadow, Glacier Point, Taft Point, and Mirror Lake.