Tuesday, June 1, 2010

Having a Blast in Fort Rock Basin - Part 2, Fort Rock

A trip to the Fort Rock Basin wouldn't be complete without a visit to Fort Rock State Natural Area, home to Fort Rock itself. Known as a tuff ring, Fort Rock was formed somewhere between 50,000 and 100,000 years ago when the fire in the earth's belly reached-up and encountered the moisture of a massive pluvial lake that existed in the region then.

Somewhere between 50,000 and 100,000 years ago basalt magma rose high enough through the earth's crust to encounter the wet muds lying below the bed of an ancient pluvial lake. The water in the mud vaporized in an instant, blowing the basalt through the lake bed and high into the air. As lava and ash rained down they formed a ring around the vent's opening, creating an island of tuff and ash in the lake. The steam explosions also loosened chunks of the black and red lava bedrock from the even older Picture Gorge Basalt flows under the lakebed, incorporating them into the layers of the new island. Over time, the lake receeded but not before beating against the sides of the island for thousands of years, erroding away the softened ash layers, revealing terraced cliffs around the outside and flooding the interior through a hole it ate in the southern exposure.  What's left is a nearly mile-wide, 200' tall capital "C" in the middle of an otherwise flat desert.

These porous, sponge-like surfaces point to gases escaping through the material of the forming island.

Paintbrush, Eriophyllum and host of other hardy flowers eek out an existence on the floor of the ring's interior.

Looking out of the opening in Fort Rock from the interior.  The town of Fort Rock can be seen in the distance.

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