. . . I've been told that I write novels for email messages. Perhaps this is the way to go. I'll try to make each entry, or Gemstone, a "precious" one. On mediocre days, all I might be able to produce is a "semi-precious" entry. In any case, an entry might be a "neat" Gemstone--something that is uniquely mine.

Saturday, July 10, 2010

Some Sedona Geology

Rocks in Red Rock Country are old. From the bottom to the top layer, you can observe about 80 million years of sediment deposition. It's like a giant layer cake with each layer being its own type of rock (sandstone, limestone, siltstone). Each layer was deposited in its own geologic era. Some layers were deposited in shallow seas, some in river deltas and flood plains. Some layers are hardened sand dunes. All of these strata were laid down, one on top of the other, during the Paleozoic Era. During this era fishes dominated the oceans and plants and amphibians were just starting to live on land.

About 350 million years ago the area that is now Sedona was covered in an ocean. Water would fill the area and then retreat over and over again for many eras. Seashores, lake beds, and sand dunes would build up and then erode away.

The red sandstone is evidence of the old sand dunes and beach deposits from long before. Wind would shift the dunes and create patterns of lines called cross beds. Eventually the dunes were cemented into sandstone by iron oxide (causing the red color) and calcium carbonate.

About 225 million years ago the tectonic plates in the region collided and slid. To the north, the Rocky Mountains were pushed up. But in the region that is now Sedona, the Pacific and North American plates slid alongside each other (this is now evident on the southern coast of California with the San Andreas Fault). Eventually, the heavier plate sank and lifted the lighter plate up, creating the Colorado Plateau north of the region.

The Arizona portion of the plateau’s edge is called the Mogollon (MUH-gee-yon) Rim. During this tectonic ballet of sorts, volcanic activity was abundant. Eight million years ago, a volcano erupted with massive flows of lava, leaving black-gray basalt over the red sandstone.

I can’t wait to explore the area and discover the different rock formations with creative names such as “Coffee Pot,” “Snoopy,” and “Bell Rock.” There is something truly relaxing about looking at rock formations and finding shapes within them.

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