What do these gates do??

[Sierra Lady]

^ I'm no geologist, but it's volcanic rock. MM is a dormant volcano.

[ofset]

Honesty, I rode up 14 once with a buddy of mine that is a Geologist and I asked him the same exact question about that same exact spot on that same exact rock that you see riding up 14. I too was fascinated by what could have caused that. He basically said what SL said. It's a volcano and that was caused by eruption. Crazy stuff

[M2M]

Mammoth's a volcano ???

[mspamelablythe]

I'm starting to see some potential in this thread....

[onegoodturn]

MM is a dormant volcano.

How dormant???

[therealme]

MM is a dormant volcano.

How dormant???

The most prominent geological feature in the area, 11,053-foot Mammoth Mountain is a dormant composite volcano formed by a series of eruptions between 220,000 and 57,000 years ago. Steam-blast eruptions occurred from vents on the north side of the mountain as recently as 700 years ago.

[onegoodturn]

MM is a dormant volcano.

How dormant???

The most prominent geological feature in the area, 11,053-foot Mammoth Mountain is a dormant composite volcano formed by a series of eruptions between 220,000 and 57,000 years ago. Steam-blast eruptions occurred from vents on the north side of the mountain as recently as 700 years ago.

Most intelligent post of the year so far...

[Mick]

Honeycomb weathering, not necessarily volcanic, not entirely understood, see:

http://zschierlphotography.com/tag/weathering/

and more academically:

http://www.tafoni.com/Bibliography_file ... hering.pdf

And many pretty images:

https://www.google.com/search?q=honeyco ... g&tbm=isch

[Sierra Lady]

^ Great stuff, Mick...thanks for the geo-nerd links! I love learning new things!!

So I looked up "California tafoni" and found this link with photos of the tafoni in Bishop Tuff!!

http://www.nvcc.edu/home/cbentley/geobl ... -time.html

That's tafoni, peppering the Bishop Tuff on the volcanic tableland north of Bishop, California. I went there in September as part of a weeklong GSA Field Forum. Tafoni is a distinctive weathering pattern presumed to be caused by salt weathering, often in sandstones. This particular example wasn't in a particularly salty location, and the rock being weathered was the Bishop Tuff, a welded volcanic ash deposit. But it's clearly the tafoni pattern:

[pkerr]

Speaking of volcanoes...
Here's the latest forecast...




I believe CyberK did this forecast.

[SkierBob]

^^ I'll guess

Air/gas bubbles in the magma when it solidified

[ucdcrew]

Without looking up close, I'm gonna go with Mick's answer for the win. I got some extra time off for doing such a good job this year (no joke, time off award), so maybe I'll be up to look in the near future! See, it pays to work hard and not complain.

[Spirit Tree]

Don't know where all of you have been on this forum. Those are mortar holes aka grinding holes the vertical variety. They were used when the wind was blowing from the other side of the rock creating an eddy effect; keeping all the contents positioned in the bowl....
Just ask Windy....

[Washoe Zephyr]

Now that the rock formation question has been solved( thank you all). I now pose another...

what does this mean?

[Flynride]

....