Through Yosemite National Park’s glaciated landscape, Half Dome, one of Yosemite’s iconic domes, stands out the most. Despite the name, Half Dome was not actually cut in half. The northwest side of the dome looks like it was cut in half, and for a while geologists thought that when the glaciers came through the valley, they did indeed greatly erode the dome. Even the local Native Americans thought that the dome was cut giving it the name ‘Tis-sa-ack’ meaning ‘cleft rock.’ However after further study, geologists came to the conclusion that at least 80% of the northwest side of the dome still remains.
Half Dome is about 87 million years old and is considered the youngest plutonic rock in that area. Most of Yosemite’s bedrock is considered to be granite. Half Dome is indeed granitic, but it is not a true granite. Officially, Half Dome is made up of granodiorite, a type of granitic rock that contains more plagioclase feldspar than orthoclase feldspar. It also contains more dark crystals because of its greater plagioclase content giving it an overall darker shade. It is less siliceous than the true granite that the park also contains.
You can actually reach the top of Half Dome without being a climber. The park service maintains a route called the Half Dome Cables Route Hike. This hike starts at the valley floor and goes for 8.2 miles (13 km) straight to the top of Half Dome with an overall elevation gain of 4,800 feet (1463 meters). Most of the trail is just steep hiking through the forest; however the last 400 feet (120 meters) of this trail is a steep ascent between two steel cables that are run though iron rods struck into the rock. It is possible to do the trail in one (long!) day, however many people hike to the Backcountry campground of Little Yosemite Valley to split the hike into two sections. Visitation for this trail has reached up to 800 people per day which makes the very small cable section crowded and dangerous. The park instituted a permit system for this trail. You now must obtain a permit to go up Half Dome Cable Trail past the section where the trail meets the first smaller dome.
Image Public Domain
More about Half Dome Geology: http://geomaps.wr.usgs.gov/parks/yos/I_1639.html
Yosemite NPS site: www.nps.gov/yose/
EPA Finalizes Environmental Justice Policy Supporting Indigenous Peoples
The U.S. Environmental Protection Agency’s new policy on working with tribes became official on July 24, as EPA Administrator Gina McCarthy signed off on the agency’s EPA Policy on Environmental Justice for Working with Federally Recognized Tribes and Indigenous Peoples.