Friday Rock Blogging: Bishop Tuff

Bishop tuff outcropBut first: For shame, USGS! Falsifying documents related to the safety, or possible lack thereof, of a long-term nuclear waste storage facility! Someone will be getting nothing but lignite in their stocking this Santa’s Birthday, for sure.

Now that that’s out of the way: 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. This 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 in Southern California and as far west 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.


  1. Rana wrote:

    Okay, you should win a prize for being able to describe tuff as the “Girliest. Rock. Evar!” and have it make sense.
    You, uh, rock, girl!

  2. yami wrote:

    Well, tuff in general is not that girly; it’s only special tuffs that are pink. Where “special” means “rhyolitic”. For example, here’s a very manly gray tuff from Washington.

  3. Rana wrote:

    So that’s a tuff guy?

  4. Paul wrote:

    Nebraska is east of long valley not west.

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