Do you avid blog-readers remember the photo of the rock that I posted on Day 18, at our campsite at Rae Lakes? In case you don’t recall, here is the photo again. 

My caption was “A natural formation? I think not…”

My friend Richard D. Smith was intrigued, and sent the photo along with pertinent location information to his friend Sean Long, a professor of geology at University of Nevada at Reno, who replied with the following message:

“As far as your rock question, to me it looks like a chunk of granite, which makes up the majority of the Sierra Nevada.  The dark-colored, triangular-shaped pieces that you can see I’m pretty sure are what we geologists call ‘xenoliths’ (funny word, I know).  Basically, when the granite was molten, and intruded into surrounding rock (what we call ‘country rock’), pieces of the country rock will often break off and fall into the melt, and will then be transported along in the melt, going along for the ride.  The xenoliths look like they are made of a rock called gabbro or diorite (hard to tell exactly from a picture), so that means they probably are sourced from the lower crust of the Sierras, maybe as deep as ~20-30 km or so.  They are the ‘roots’ that the Sierras are built on.  So…this rock is pretty neat, lot’s of history just in one little piece!  Pieces of the lower crust embedded in a granite melt that then traveled up and was emplaced and cooled and crystallized in the upper crust, and has now been eroded to be at the surface today.  Gotta love geology!”

FYI, the rock is about two feet wide. This made me very happy that I had decided to snap a photo of it. Think of it as a High Sierra jack-o-lantern. I hope you all had a happy Day of the Dead, Hallowe’en, All-Saints’ Eve, Samhain, or whatever other holiday you celebrated or may be celebrating around now.

Laurie