Stop 5
Weathered
Serpentinite Exposures and Blueschist Facies
Stop 5 is southwest from the
airport. (Google Earth)
Temperature and
depth of burial for different metamorphic facies.
Stop
5
Stop
5 is at an exposure of serpentinite just northeast of the El Rancho Escondido
property. The property had serpentinite outcrops which can contain asbestos so
most of it was removed, this makes exposures harder to find. At this stop its
heavily weathered and all you find are some pieces with a pale greenish hue.
You can see this in the closeup picture.
Stop 5 is in the
serpentinite unit.
Closeups of
heavily weathered serpentinite. Although it’s quite weathered, in the 1st
picture you can see the serpentinite fabric. The 2nd picture shows
the more common rubble found here with the greenish hues.
Enroute
to Stop 6
There are
excellent exposures of blueschist in Cottonwood Creek, which runs parallel to El Rancho Escondido road from the Middle Ranch Road to the
El Rancho Escondido Property. The easiest access is from Middle Ranch Road and
is generally ok for 4wd vehicles with good ground clearance but not for the
vehicles we take on the group fieldtrips. So instead, we go to Little and Shark
Harbors to see the blueschist facies rocks.
If you’re
feeling adventurous and have the proper vehicles (at least 2 are best), you can
continue up Cottonwood Creek all the way up to Cape Canyon Road which connects
to Airport Road. The road can be hard to follow in places and its condition is
variable from season to season, especially after heavy rains.
Blueschist
exposures in Cottonwood Creek
A bison near the switchback
on Middle Ranch Road between Cottonwood Beach and Shark Harbor.