San Diego's peak
mining period occurred during the Julian gold rush of 1870. This
occurred in the rock known as the Bedford Canyon Formation, or
known locally as the Julian Schist. It is named for a series of
metamorphosed sedimentary rocks first studied in the Julian area by
F.S. Hudson in 1922.
The schist contains quartz veins, some of
which contain significant amounts of gold that was the result of
the gold rush to this region. Gold found in these quartz deposits
occur as lenses or veins. These veins can be as small as a fraction
of an inch in width; the local Stonewall Mine, on the other hand,
hit a vein twenty feet wide!
At the indicated coordinates listed above
just off of Sunrise Highway (S-1) you will be near a parking area
used for installing or removing tire chains. The schist at these
road cuts consist of a fine-grained mica schist and quartzite,
though somewhat weathered. Farther down the road between the green
mile markers 34.0 and 33.5 you will see some additional but more
impressive road cuts exposing the Julian Schist
formation.
The metamorphic rocks exposed at these
locations represent sands and mud that accumulated at the shoreward
fringe of an ocean basin. They later were compressed and subject to
high temperatures (hypothermal) and pressure. Eventually they were
uplifted through mountain-building (tectonism) and exposed some
5,000 feet above sea level. These Julian deposits differ from the
Sierra-Nevada gold bearing deposits which were mesothermal in
origin and formed under low pressures.
TO LOG THIS
CACHE:
1) If these sedimentary layers
were once buried deep, how did they get here? And why are some
almost twisted vertically?
2) Try locating a quartz "vein",
how wide is it?
To log
this cache e-mail me the
answer
HERE
.