Joshua Tree National Park - Arch Rock
Posted by: 
TerryDad2
N 33° 59.184 W 116° 00.941
11S E 590915 N 3761084
Quick Description: This natural arch is located along a well posted geologic nature trail that starts in the White Tank Campground. The trail ranges from loose sand to hard rock with steps. There are great signs posted along the trail with additional geologic information about the area.
Location: California, United States
Date Posted: 8/24/2006 7:52:32 PM
Waymark Code: WMN9X
Views: 53
Long Description:This natural arch formed in the White Tank Granite. This igneous
rock is thought to have pushed its way up into the surrounding
Pinto Gneiss between 135 to 155 million years ago creating a large
pluton (see other earthcache). This pluton cooled slowly allowing
the relatively large crystals of quartz, feldspar, and biotie to
form.
Through a variety of erosional processes, an arch was formed in
the granite. Jointing (see other earthcache) created lines of
weakness in the massive granite pluton. Water dissolved the rock
surface and seeped into small cracks where it froze and expanded
causing the small cracks to get larger. By chance, the result of
the erosion created the arch.
Visit Instructions:
A log will require a recent photograph at the coordinates. Some
of these locations will be placed for the scenery, so a gpsr will
just ruin the picture.
If you don't have a digital camera post a descriptive log.