This open space area called Woodson
Mountain (or Mount Woodson), once called by natives as the Mountain
of Moonlit Rocks and by early settlers as Cobblestone Peak, now
appears on maps as Woodson Mountain in honor of Dr. Woodson who
homesteaded some nearby property in 1875. Woodson was a surgeon in
the Confederate Army during the Civil War and after achieving local
prominence, the mountain was named in his honor. It currently is
part of the City of
Poway trails system.
Rocks from this mountain were used to
construct the famous Ramona Castle or the Mt. Woodson Castle.
Designed by John Vawter and Emmor B. Weaver, the Mt. Woodson Castle
combines English cottage and French castle influences. It is now
part of the Mt. Woodson Golf
Club.
A California Conservation Corps (CCC) camp
was built on 40 acres of land at the base of Woodson Mountain in
1933. In 1934 some 300 men were stationed at the camp and were in
charge of building the road to the top of the mountain as well as
lookout towers around the county and a forestry station at Woodson
Mountain.
EDUCATIONAL INFORMATION
This prominent peak with its distinctive
boulder strewn appearance stands at 2894’ and appears much
different from surrounding peaks in the county. You may have
wondered where did all these boulders came from? Well, they were
actually always there! These boulders formed in place by
spheroidal weathering, which is a form of chemical
weathering in which concentric shells of decayed rock (ranging from
a few millimeters to a couple meters, WP1& WP2) are successively
loosened and separated from a block of rock, transforming angular
blocks into round boulders as you see today.
These boulders are remnants of rock that
cooled below the earth's surface. As cooling progressed the rock
contracted and cracked (WP5). Millions of years
later, after uplift brought the rock closer to the surface, warmer
temperatures, elevated atmospheric carbon dioxide, and decaying
vegetation combined with rainfall to chemically weather the
surfaces of the rocks (WP4). The degree of
weathering was controlled by the ability of these solutions to
penetrate rock. As the decomposed material was stripped away, large
round boulders were left behind to form boulder strewn hills like
Woodson Mountain.
The light colored bedrock of Woodson
Mountain is a type geologist’s call Woodson Mountain
Granodiorite (WP3& WP3). It has speckles of
mafic minerals (dark-colored minerals rich in iron and magnesium),
such as biotite (black mica) and hornblende. Granodiorite is
classified by the unique amounts of the framework minerals know as
quartz (30%), plagioclase (50%), and alkali feldspar (20%) that
compose it. This type of rock weathers into boulder strewn slopes
rather than smooth slopes, perfect for the local rock
climbers.
At these views of Highway 67
(WP6
& WP6) a road cut shows
that weathering along joints forms large, mostly unweathered rock
surrounded by more weathered, softer, browner material which is
easily eroded, leaving the least weathered rounded rocks in
place.
To LOG
this CACHE:
1. Measure the "pealing" thickness of this example of a
weathering boulder located at WP2.
2. Submit with your
log a photo of yourself and GPS at WP5,
micro-fractures.
To log this cache e-mail me the
answer HERE.
TECHNICAL
Spheroidal weathering:
(“onioning”) is a form of chemical weathering, in which
concentric shells completely surround a corestone. Causes of
spheroidal weathering include the following hypotheses; expansion
(several types), unloading, constant volume alteration, Liesegang
phenomena, micro-cracks, and possibly several other mechanisms. The
following sources were used to generate this cache.
Here's a list of references and additional reading
material:
- Beck, C.D. 2004. On
Memory’s Back Trail: A Story History of Ramona and the
Backcountry of San Diego County. Backcountry Press.
297p.
- Clifford, H.J., F.W.
Bergen, S.G. Spear, & D.M. Burns (ed.) 1996. Geology of San
Diego County: Legacy of the Land. Sunbelt Publications.
175p.
- Kennedy, D. 1999. San
Diego County Climbing Guide. Deadpoint Press.
177p.
- Ollier, C.D. 1971. Causes
of spheroidal weathering. Earth-Science Reviews. Vol. 7,
Issue 3, p. 127-141.
- Ruth, L. 1982. The Ramona
Castle: Irene Amy Strong’s Home and the Craftsman Movement.
The Journal of San Diego History. Vol. 28, No.
3.
- Shad, J. 1992. Afoot
and Afield in San Diego County. 2nd Edition. Wilderness Press.
304p.
- Walawender, M.J. 2000. The
Peninsular Ranges: A Geological Guide to San Diego’s Back
Country. Kendall/Hunt Publishing. 114p.
