The origin of the geological landscapes of the park have been under debate since 1865. At that time, Josiah Whitney, then chief geologist of California, proposed that Yosemite Valley is a graben: a downdropped block of land surrounded by faults. John Muir proposed that Yosemite Valley and Hetch Hetchy Valley were formed purely by glacial action. In 1930, François E. Matthes proposed a hybrid hypothesis, where most of the depth of the valley was gouged by water erosion, the rest by glacial action. The glacial action also claimed to have widened the valley. More recently, the debate has been reopened by Jeffrey Schaffer, who suggests that the role of glaciers and other erosion processes has been dramatically overstated. Schaffer states that Yosemite Valley above 5600 feet (1700 m), for example, has changed relatively little in the past 30 million years. Other than being slightly larger, if one could look back in time and see them, the major features would be recognizable to the modern eye. Schaffer believes that the numerous joint planes have had the greatest impact on the geomorphology of the Park's major features. This is in contradiction to the consensus view that huge highly abrasive glaciers acting on joint planes combined with a great deal of uplift over just the past couple million years was the primary shaping force of the features (such rapid uplift would have greatly accelerated all types of erosion). See also Sierra Nevada bibliography for further reading Cathedral Peak Granodiorite El Capitan Granite Half Dome Granodiorite Kuna Crest Granodiorite Sentinel granodiorite References External links Origin of Yosemite Valley, Chapter 4, Glaciers of California, by Bill Guyton Geology of the National Parks: Yosemite National Park's Geology (USGS online exhibit) The Geologic Story of Yosemite National Park by Dr. N. King Huber (USGS, 1987) USGS Bulletin 1595. Complete text online The Geologic Story of Yosemite National Park (1987) by N. King Huber Geology of Yosemite National Park Yosemite National Park Yosemite area Yosemite Articles containing video clips