Calavera Hills Volcanic Plug
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A volcanic plug, also known as a volcanic neck or lava neck, is a landform created when magma (lava) hardens within the vent of an active volcano. This magma literally “plugs” the vent.
The build up of pressure could sometimes lead to an explosive eruption, or the heat and pressure from below could reduce so that the magma inside the volcano's vent cools and solidifies.
When the volcano becomes extinct and the surrounding rock starts to erode away, the erosion-resistant "plug" is all that is left behind producing a distinctive upstanding landform.
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Some of these plugs appear as a solid rock, others form distinct columns. Morro Rock in California, Little Devils postpile in Yosemite, and Devils Tower in Wyoming are good examples.
The Calavera Hills Volcanic Plug
Mount Calavera is 513 feet high, but is not really a mountain; it is a 22 million-year-old volcanic plug. Mount Calavera is one of only three volcanic plugs in Southern California. In the early 1900's through the 1930’s, the ancient plug was mined for gravel. The mining stripped away west face, exposing the plug. What is left is an excellent view of what was once the inside of this volcano.
From the Earthcache coordinates, look south east, past the lake to Mount Calavera. The top of the Mount is about .33 miles from this point.
Logging Requirements and Questions:
Please send an email with the following information....
1. The Text "Calavera Volcanic Plug” on the first line.
2. The Number of People in your group.
3. An estimate of the height of the plug, not the mountain top.
4. Is the Calavera plug, a “rock shape” like Morro Rock or “Columns” like Devils Postpile?
5. OPTIONAL: A picture of you, your group or your GPSr with the volcanic plug in the background.
* Diagram of a diatreme with its maar-crater illustrating its exhumed position (land surface today) as a volcanic neck following its erosive exposure. Source unknown. (web address: http://written-in-stone-seen-through-my-lens.blogspot.com/2011/01/ship-rock.html)