The Sierra Nevada is a huge westward tilted block. The slope has allowed the rivers draining the mountain range to carve deep gorges, some deeper than the Grand Canyon (Kings Canyon to the south is about 8,000 feet deep!). The depth of the Merced is more like 2,000 to 3,000 feet deep downstream of Yosemite, and in any other setting in most any other state, this would be enough for the establishment of national parks and the like. Instead, it is "just" the preliminary canyon one must pass through before arriving at Yosemite.
The carving of such deep canyons can have serious geologic consequences for society. The slopes of such canyons are inherently unstable, and mass wasting (landsliding) is a constant hazard. The building of roads and railways adds to the instability by undercutting the already steep slopes. Such is the case with Highway 140. CalTrans has struggled for years to prevent the collapse of a slope near the village of El Portal. In 2006, the slope flicked away the mitigation efforts and collapsed onto 600 feet of highway. The Ferguson Slide, as it is called, closed the highway for months and caused economic hardship for the surrounding communities. Two temporary bridges were constructed to cross the river and circumvent the huge slump. Decisions have yet to be reached regarding the permanent disposition of the highway.
|The Ferguson Slide. 600 feet of Highway 140 is buried under the rocks.|
gloom and doom post regarding fires, rejuvenation does indeed occur, as many of these slopes have been cleared of brush and chaparral by repeated wildfires, allowing for dense concentrations of wildflowers.
We passed El Portal, and then the Yosemite View Lodge. The name is not totally dishonest; the boundary of the national park does indeed lie a few yards east of the hotel complex, so the view of the granite slope beyond is indeed a view of Yosemite. But it is not yet the iconic valley with Half Dome and El Capitan and Yosemite Falls. It is pretty, though, and the Merced River makes a dramatic dash through the maze of gigantic fallen boulders.
but not tomorrow). In Yosemite, we are sitting within a former magma chamber, under the volcano. As such we are exploring the inner depths of an extensive magma system, brought to light by long periods of uplift and erosion.
In a coming post, we'll see how Yosemite looked on Saturday.