Neenach Formation - Other Half of Pinnacles
A
cache
by TerryDad2
Hidden:
8/15/2005
Size:
 (Not chosen)
Difficulty: 
Terrain: 
(1 is easiest, 5 is hardest)
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This is a stop along a county highway where you can see outcrops of
the Neenach Formation (the other half of the Pinnacles NM) near the
top of the hill to the east. Don't expect too much; there's a
reason this part didn't become a national park.
 
Outcrops of the Neenach Formation are located on private
land. This Earthcache is to give perspective to the Pinnacles
Eartchcaches (GCPRKJ and GCPRKP) about 195 miles to the north. There
is safe ample parking by the mailboxes on the west side of the
road.
Near the top of the hill to the east of this stop are a few
outcrops of the Neenach Formation. It is a dark reddish to purplish
brown andesite. Unfortunately, because all the outcrops in the area
are on private land you can't get a close look at them.
From a distance, the weathering and geomorphology of these
outcrops looks similar to the pinnacles of the Pinnacles National
Monument, only much smaller.
The formation of these rocks begins about 60 million years ago.
At that time, an oceanic plate (a piece of the crust of the earth)
called the Farallon Plate and the continental North American Plate
were moving toward each other. Instead of crunching together like
two cars, the Farallon Plate was directed down into the earth while
the North American Plate stayed on top. This plate movement of an
oceanic plate diving down under a continental plate is called
subduction.
During the subduction, portions of the Farallon Plate were
scraped off the top and pushed up against the edge of the North
American Plate forming much of the north-south coastal mountains.
As the Farallon Plate went deeper in to the earth, it began to melt
under the North American Plate. The melting Farallon Plate formed
large amounts of magma (melted rock) that moved up through weak
areas along the edge of the North American Plate forming
volcanoes.
It is estimated that the volcano that formed became active about
22 to 23 million years ago, the Miocene. While it was active, it
formed an estimated 8,000 foot high mountain, 15 miles long and 5
miles wide. David Warburton of Florida Atlantic University puts
that as a little smaller than Mt. St. Helens.
At some point, the North American Plate migrated over the
spreading center that was the boundary between the Farallon and
Pacific Plate. The spreading center is a plate margin where the
plates are constantly moving away from each other and magma is
continually filling in the space between them. Once that happened,
the Farallon Plate no longer existed, and the volcano became
extinct.
Instead of moving toward each other, the Pacific Plate was
moving northwest relative to the North American Plate. This changed
the plate boundary to the transform fault we are familiar with
today. As it happened, the volcano ended up straddling the fault
line that formed between the plates.
It is estimated that the Pacific Plate has moved approximately
1.5 inches per year resulting in the portion of the volcano on the
Pacific Plate moving 195 miles northwest to become the Pinnacles
National Monument relative to the rest of the volcano that is on
the North American Plate, where you are now.
An additional location to see outcrops of the Neenach is at N34
46.639 W 118 40.409. The outcrop is up the hill to the south way
across the field on private land. I would suggest binoculars for
this one.
Logging requirements:
Send me a note with :
- The text "GCQ5FZ Neenach Formation - Other Half of Pinnacles"
on the first line
- The number of people in your group.
- where you see outcrops of rock similar to the one a the
coordinates.
- Why the outcrops tend to be at the elevation they are and why
you think the Neenach formation doesn't look like the
Pinnacles.
The above information was compiled from NPS
documentation and the following sources:
- National Geologic Map Database,
USGS, Summary of Citation: Neenach Publication: Dibblee, T.W., Jr.,
1967, Areal geology of the western Mojave Desert, California: U.S.
Geological Survey Professional Paper, 522, 153 p., (incl. geologic
map, scale 1:125,000)
(http://ngmdb.usgs.gov/Geolex/Refsmry/sumry_11424.html)
- Geology of National Parks, GLY 3164, © 2004 by
David L. Warburton
(http://www.geology.fau.edu/Resources/CourseWebPages/Fall2004/GLY3164/NPPINNNM.htm)
- San Francisco Bay Area Network I & M
Program Monitoring Report: Phase I October 2002 version 8/15/2005
Jennifer Bjork
http://www2.nature.nps.gov/geology/parks/pinn/#geology
- Stanley, Richard G., et. Al. , 2000, Locaitons
and Ages of Middle Tertiary Volcanic Centers in Coastal California,
Open-File Report 00-154, USGS
http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_california.html
Additional Hints (
Decrypt
)
Decryption Key
A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z
(letter above equals below,
and vice versa)
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Ernq gur Cvaanpyrf qrfpevcgvba. Fraq n abgr JRNGURE be abg lbh ner fher bs gur nafjre.
(Decrypted Hints)
Find...
 Neenach.jpg
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Current time: 11/22/2009 9:48:14 AM
Last Updated: 11/21/2009 5:06:37 PM
Rendered: From Database
Coordinates are in the WGS84 datum
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