Rock gone bad

This weekend I went on a hike/geology talk led by a former SOU professor at Pilot Rock, which is south and east of Ashland, in the Cascade-Siskiyou National Monument. Pilot Rock is part of the Western Cascades, which are the older (40 million years old) foothills to the High Cascades, which are 3-5 million years old. Pilot Rock is made up of igneous volcanic rock. The definition of igneous rock is molten rock that has cooled, either above the crust of the Earth, as lava, which is called extrusive igneous rock, or underneath the crust, as magma, which forms intrusive igneous rock. (Magma and lava are both molten rock, but whether it is above the crust or not determines which the molten rock is called). Pilot Rock is an extrusive igneous rock called basalt, but while the lava did break through the crust, it did not erupt out of the volcano. As the years went by, the softer rock that made up the outside of the volcano eroded, leaving the basalt plug of the volcano vent that has now become the prominent feature we know as Pilot Rock. Below are come pictures of Pilot Rock and the geology hike.

The group hiking to get a good view of Pilot Rock

Pilot Rock

Close-up of Pilot Rock

Another fun fact is that the bright green lichen you can see near the base of Pilot Rock is called Pleopsidium- you can tell this from a distance and be almost guaranteed to be correct. 

After the geology talk part of the hike ended, one of the other grad students in my cohort, Shauna, and I hiked/scrambled to the top of Pilot Rock. While it is considered a hiking trail, the last section (maybe 1/4-1/2 mile) is all class 3-4 scrambling. The other, steep side of Pilot Rock that you see in the pictures is indeed a local rock climbing spot with several multi-pitch climbs, so hopefully I'll be able to write later about the experience of Pilot Rock from the climber's side. But the hiking side was a lot of fun, and from the top, one can see Mt. Ashland (about 45 minutes south, southwest of Ashland), Mt. McLoughlin (the peak north and northeast of Ashland; I've put up pictures of McLoughlin in previous posts), and finally, Mt. Shasta, the peak in northern CA, about an hour and 1/2 south. Mt. Shasta, as you can see in the picture below, has already received significant snowfall, as it is around 14,000 ft in elevation.

Shauna and I at the top of Pilot Rock

Mt. Shasta

If you look at the land beneath Mt. Shasta, you can see that it looks like a lot of mini-mountains or hills. This is the leftover landslide deposits left behind from the eruption of Mt. Shasta. Jad, the SOU professor, compared this phenomenon to a air hockey table being lifted up on one side and slanted, and then a puck sliding along the table. This is exactly what happened to all the rock that made up the landslide deposits: the pressure from the eruption created a layer of air between the side of the volcano and the erupted rock, allowing it to slide that much faster and further, which resulted in a multiple, massive deposits of landslide rocks below Shasta.

So a quick review: Pilot Rock is a plug from an ancient volcano, specifically called basalt, which is an extrusive igneous rock formed from cooled lava. It is part of the Western Cascades, which are around 40 million years old, and are the foothills to the younger High Cascades. And even if you don't know what type of rock formed the area where you live, at least you can know that rock gone bad is the basis for soil.