Friday Rock Repost: The Bishop Tuff

This is an outcrop of Bishop tuff, an ash deposit created 760,000 years ago when the Long Valley Caldera exploded - though “exploded” is, if anything, an understatement. The photo was taken 15 miles (25 of your Earth kilometers) away from the eruption; it contains no persons for scale, but the outcrop is about 10m high. Ash deposits from the same eruption are found all over Southern California and as far east as Nebraska.

Tuff is what happens when a pile of hot ash (”ash”) and fragments of exploded crap (”breccia”) consolidates and hardens under its own heat and weight. If the proportion of exploded crap is too high, the result is more properly called a volcanic breccia, but the Bishop tuff is mostly welded ash. If you look at this formation up close, you’ll see that it is pink (for the same reason that granite is pink; it’s made of the same stuff) and sprinkled with little angular fragments that are often sparkly. Girliest. Rock. Evar!

And I hereby proclaim the Bishop tuff to be the tiara of the Sierra Nevada, and the Sierra Nevada Mountains to be the Princess of California, long may they collectively smile and wave in their mountainy way. The End.

Update: Kim suggests that the Gassetts Schist is the sparkly tiara of the Taconian Orogeny, and therefore the Green Mountains are the Princess of New England. I feel a meme coming on... what other rocks are royalty?