Monday, April 11, 2011

Garry Gazes at Granite, a prequel to "Horton Hears a Who"

"What color are rocks?" I ask my students, with the intention of highlighting stereotypes about geology. "Gray" is the inevitable answer. I then have them look around the lab, with the many rock samples strewn about, and they immediately realize that rocks occur in many shades. But why is gray always the answer?

I usually assume that it is because granite is made of light and dark colored minerals that appear sort of gray at a distance, and granite is the rock that my students are most likely to see in streambeds around our area, but I have come to realize that this doesn't fully explain things. Most casual visitors to Yosemite and other Sierra Nevada destinations rarely actually see granite (or granitic rocks; there are many kinds). Look at the boulder in the picture of Ribbon Falls above. It's a big chunk of El Capitan granite that should be nearly white in color (see the last picture in yesterday's post). Why isn't it? It's covered! Gray life, and lots of other colors too!

My students must have been amused to see me on my knees, hunched over like a bar denizen who's had a bit too much to drink. I was grabbing some pictures of the complex miniature ecosystem that exists on every boulder and rock in Yosemite (and pretty much everywhere else). There are the "trees" of this little environment, the mosses (below). I assume they are 'rooted' in the weathered clay, or in the damp spaces left by departed mica grains;
On a finer scale, there is the 'underbrush', the lichens, the symbiotically joined fungi, algae and cyanobacteria that often coat the rock surfaces. They are a colorful addition to the landscape.
It's intriguing how many complex relationships exist on literally every rock littering the surface of Yosemite. It took me only a few moments of crawling to find numerous colorful examples.
Through a macro setting, the bizarre microworld becomes even more complex (click in the picture to enlarge). "Horton Hears a Who"? I could almost imagine the even smaller creatures living in the small openings! They didn't speak to me today, so you don't need to lock me up... just yet.
Yosemite National Park has undertaken an assessment of lichens in the park, with more than a hundred species cataloged, and an estimated 500 kinds yet to be discovered. Besides being interesting in and of themselves, the lichens also serve as a way of assessing air pollution damage in the park. Because they are slow-growing, they also serve as a method of dating the surfaces of glacial moraines in Yosemite and other alpine regions.

Yosemite is not the only place where numerous lichens can be found; the picture below (from a previous post on lichens in the foothills) shows a veritable palette of colorful lichens in Mojave National Scenic Area. It's one of my favorite photos.
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