Oh! ...just because it is part of the Marin Headlands Terrane
doesn't mean that it is in Marin! It is in San
Francisco!
I grew up in this neighborhood, thinking this geological feature
was the result of glacial forces, but I was wrong - I know better
now!
Best to view this during daylight hours - the park is closed
between 10pm and 6am.
What is/are
"Slickensides"? Slickensides refers to the polished but
striated (or scratched) marks on a rock, resulting from a shear
force from a fault that appears to polish the face of a rock -
making it look wet or "slick".
This location is on the leading edge of the Marin Headlands
Terrane, which
buckled up against the Alcatraz Terrane leaving the Fort Point
Mélange
in-between. This force caused slippage, making this fascinating,
smooth wall!
This geological feature is fairly unique as it isn't the usual
type of rock found as a Slickensides - extra credit if you know
what type of rock you find here :-)
For credit and to log this EarthCache: please send an email
which indicates your estimate on the height of this slickensides.
For the log, provide the number of people in your group and provide
a URL/link for another Web Site that discusses Slickensides, or
include in your log some story about where you have found
Slickenside formations other than this one.
There are additional fragments on top of the hill - go to
Randall Museum and hike up the hill to the following coordinates to
find much smaller fragments of slickensides (and a gorgeous view of
the City):
N 37 45.904
W 122 26.389
N 37 45.910
W 122 26.369
N 37 45.899
W 122 26.338