Monday, March 5, 2012
Geology Tour Road Redux: Mighty Old Rocks
On Valentine's Day, we packed a lunch and took off for one of our favorite spots, the Geology Tour Road in Joshua Tree National Park. It was a blustery day--cool air, warm sun, and hosts of beautiful clouds passing through.
We pulled over and hiked a short distance to what we think was the Towers of Uncertainty area. There used to be a sign marking it, which we didn't see on this trip. Anyway, it didn't matter--we just enjoyed the boulders and the uncertainty of it all.
Balance Rock, above, is a landmark on the way to Malapai Hill, below. The hill is made mostly of black basalt. It's younger rock than the surrounding monzogranite boulders--maybe two or three million years old as opposed to 85 million years old.
Finally, the local Methuselah of the rock world is Pinto Gneiss ("Nice")--at around 1.7 billion years old, probably the oldest rock in the park. Gneiss is metamorphic rock, formed under great pressure; monzogranite and basalt are igneous rocks, formed from cooled magma. According to the Geo Tour Road brochure, "the alternate banding of light and dark minerals defines a gneiss."