Friday, March 25, 2016
A Sight That Overwhelms: Dante's View and a Sense of Scale
"Mos Eisley spaceport. You will never find a more wretched hive of scum and villainy.").
The lack of vegetation is a boon to the geologist, of course. The exposures of bedrock are unparalleled, revealing a great deal about the geologic history of this part of the world. And it is a strange story. Much of the mountain range is composed of the Black Mountain Metamorphic Complex, a selection of gneiss and schist sequences that reveal evidence of a titanic series of plate collisions 1.7 billion years ago. At that time, North America was hit by a series of terranes, island systems maybe the size of New Zealand or California. The collisons produced a mountain range hundreds of miles long that would recall the coastal ranges of southern Alaska, minus the rainforests (terrestrial life didn't arise for at least another 1.2 billion years). These rocks are related to those found in the depths of the Grand Canyon and farther south in Arizona and New Mexico.
In the ensuing years, the vast range would be eroded to a nearly flat plain, and the surface would eventually subside below sea level. Tens of thousands of feet of Paleozoic sediments covered the rocks so they lay hidden deep in the continental crust. In the last few tens of millions of years, the regional crust was stretched and extended, and the overlying rocks slid away, causing the Black Mountains to "pop up" in the geologically short stretch of two or three million years. The exposure of the deep crust was accompanied by violent caldera eruptions, and parts of the mountain range are covered by colorful ash deposits (the rocks along Artists Drive Loop are particularly memorable).