|Castle and Beehive Geysers at Yellowstone National Park, Wyoming|
|Yosemite Falls from Swinging Bridge in Yosemite Valley|
It's hard to think of two parks more different from each other. Yellowstone, with geysers, hot springs, bison, and moose. Yosemite, with huge vertical cliffs of granite and high alpine peaks. In Yosemite, the bears break into your car. In Yellowstone, the bears occasionally eat you.
|Sunset in Yosemite from the Gateway View|
|El Capitan in Yosemite Valley|
|Lassen Peak and Brokeoff Mountain, an active volcanic center in the southern Cascades Range|
The subducting slab of oceanic crust in Cretaceous time was heated, and water that was released changed the melting point of the rocks at the base of the continental crust. The masses of molten rock worked their way up into the upper crust. Some of the rocks erupted at the surface as large Andean-style volcanoes, or as rhyolitic caldera eruptions. The chain of volcanic features is called a magmatic or volcanic arc. The surface may at times have even resembled Yellowstone, although present day Lassen Volcanic National Park or Mt. Shasta provides the best analog. But deep in the crust the rock was cooling slowly, developing into large crystals of quartz, feldspar and mica, then principle minerals of granite and related plutonic rocks.
|El Capitan Granite, with gray-looking quartz crystals, white feldspar, and black biotite mica|
Yosemite Valley provides a 3-D view of seven or eight different intrusions of granitic rock (for the purists, these include granite, granodiorite, tonalite, and diorite). Some of the rocks, principally the granite, stand out as bold cliffs like El Capitan and Cathedral Rocks. Other rocks were more easily eroded and formed recesses. The combination gives Yosemite the unique appearance that sets it apart from so many other glacially carved canyons.
When you visit Yosemite, take a moment to realize you are exploring the underside of massive volcanoes, quite literally Yellowstone or Lassen or Shasta from the inside out. It never ceases to amaze me that while the 3,000 foot cliffs are spectacular, they once were buried 4 or 5 miles deep in the crust, and that erosion has removed the missing rock (and filled our Great Valley in the process).
|Half Dome from Washburn Point above Yosemite Valley|
We've completed our exploration across the most dangerous boundary, and we are still alive! It's been several months with lots of interruptions, so you can expect a compilation of all the posts soon so you can get the whole story in one place. I hope you've enjoyed the journey!