Bill Williams Mesa Basalt EarthCache
Bill Williams Mesa Basalt
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One of the interesting aspects of discovering Arizona is that its geology is laid bare. The lack of abundant rainfall limits both vegetation and erosion making the underlying geology visible.
In Arizona’s Sonoran Desert, it is common to find large areas of exposed extrusive igneous basalt. This rock is one of the dominant building blocks in the earth’s crust. The rock is usually dark grayish brown to black. It is comprised mainly of calcium rich feldspar (gray) and various pyroxenes (dark) minerals. It is not unusual to find small collections of lichens growing on the northern side of larger porous basalt rocks feeding off the small amounts of water retained in the rocks.
A typical basalt rock can be relatively uniform and smooth comprised of small uniform granules. This is known as aphanitic basalt. Other basalt rocks will appear to have holes formed from gas bubbles. This is known as vesicular basalt. The mineral composition of the two types is mostly similar with the difference caused by the conditions when the molten rock cooled into a solid. Both conditions can exist inside the same rock.
This geocache required a hike up and across Bill Williams Mesa. Most of the mesa is comprised of basalt. There is also abundant quartz. The mesa has staghorn cholla and prickly pear cacti along with mesquite and cat claw briars. Numerous javelina feed off the prickly pear and whatever else they can scrounge.
The cache can be approached in a variety of directions. All approaches will require some climbing with most of the difficult hike off trail. This is a back country geocache in the desert. Please take appropriate precautions. Bring more water than you will need. Don’t travel alone unless a highly experienced desert hiker. Always make sure someone knows where you are going. Take more water than you think you will need.
To log this cache, please proceed to the coordinates. You will find a large basalt boulder. The boulder is primarily aphanitic (smooth). However on its north and south sides are vesicular areas shaped like a horseshoe. The east side of the boulder has circular vesicular areas as well. A small boulder adjacent and south of the boulder in question has a small and recently inscribed “petroglyph” symbol.
To claim credit for this Earthcache, email the following information:
1. The text "GC2P0D7 Bill Williams Mesa Basalt" on the first line
2. The number of people in your group and the date of your visit.
3. The number of circular vesicular areas on the east face of the boulder.
4. The symbol on the adjacent rock to the south.
Please feel free to post photos of the area. However, any logs or photographs giving the answers to these questions will be deleted.
Additional Hints
(No hints available.)