erupted, bringing large amounts of igneous material in the area. These igneous deposits blanketed the region north of the Yosemite area. Some lava associated with this activity poured into the Grand Canyon of the Tuolumne and formed Little Devils Postpile (a smaller but much older version of the columnar basalt palisades in nearby Devils Postpile National Monument). In the late Cenozoic, extensive volcanism occurred east of the park area. Within the Yosemite region, andesitic lava flows and lahars flowed north of the Grand Canyon of the Tuolumne and volcanic dikes and plugs developed from faults on the flanks of Mount Dana. There is also evidence for a great deal of rhyolitic ash covering the northern part of the Yosemite region 30 million years ago. This and later ash deposits have been almost completely eroded away (especially during the ice ages). Volcanic activity persisted past 5 million years BP east of the current park borders in the Mono Lake and Long Valley areas. The most significant activity was the creation of the Long Valley Caldera about 700,000 years ago in which about 600 times as much material was erupted than in the 1980 eruption of Mt. Saint Helens. The most recent activity was the eruption of the Mono-Inyo Craters from 40,000 to 600 years ago. Uplift and erosion 10 million years ago, vertical movement along the Sierra fault started to uplift the Sierra Nevada. Subsequent tilting of the Sierra block and the resulting accelerated uplift of the Sierra Nevada increased the gradient of western-flowing streams. The streams consequently ran faster and thus cut their valleys more quickly. Tributary streams ran more-or-less in line with the Sierras, therefore not having their gradients increased. Thus their rate of valley cutting was not significantly affected. The results were hanging valleys and cascading waterfalls where the tributaries met the main streams. Additional uplift occurred when major faults developed to the east, especially the creation of Owens Valley from Basin and Range-associated extensional forces. Uplift of the Sierra accelerated again about two million years ago during the Pleistocene. However, Yosemite valley was not created by streams or fault lines (to create a graben valley), such was suggested by geologist Josiah Whitney. Glaciers shaped the Yosemite Valley, and can easily be confused with a graben valley. (Example of a graben valley is Death Valley in California) The uplifting and increased erosion exposed granitic rocks in the area