onegoodturn wrote:Sierra Lady wrote: MM is a dormant volcano.
therealme wrote:onegoodturn wrote:Sierra Lady wrote: MM is a dormant volcano.
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.
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:
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