The San Andreas Fault Zone is a major structural and
physiographic feature in California and forms the southwestern edge
of the Antelope Valley. The fault is a right-lateral
strike-slip fault, marks a transform (or sliding) boundary where
the Pacific Plate is heading Northwest relative to the the North
American Plate. This transform boundary is
locked in tension which causes deformation of the areas along the
fault. The tension is released in the form of
earthquakes which also cause deformation of the earth and
rocks.
The posted coordinates you will take to to a spot along
the fault boundary where you can see several different fault
features (deformations) that have resulted due to the powerful
movement of the San Andreas fault. Some of the features of a
fault zone that you can find are:
Sag Ponds: An area between two parallel fault zones that
has dropped, or sagged, down creating a depression that can fill
with water. Examples of sag ponds are Lake Palmdale and Una Lake in
Palmdale, Lake Hughes, Elizabeth Lake, and Jackson Lake near Big
Pines.
Fault-Controlled Valleys: A result of two parallel fault
lines lifting mountains or ridges alongside a dropped down area, or
the result of thousands of years of erosion in a fault zone. Rock
within fault zones has been weakened and is therefore easier to
erode.
Fault Scarps: Formed through the surface manifestation of
movement that occurred underground along a fault during major
earthquakes or continued movement along a specific fault zone over
a large period of time.
Fault Gouge: Rock that has been ground to a fine powder or
clay along faults is known as "fault gouge". These zones of fault
gouge can be as wide as 25 feet or as narrow as one inch. With
continued movement, solid Granite can be turned into clay as
evidenced in many places along the San Andreas Fault
Zone.
Offset Streams: Movement along a fault can offset drainage
features.
Logging Requirements: Park near at posted
coordinates along the Ridge Route and analyze the geology in front
of you and behind you. Answer the following questions in an email
to me:
1) Name at least two fault features you see here. Please
describe them and their location relative to your position.
2) Describe the rock south of coordinates. What happened to
it?
Logs that do not meet ALL of the above requirements will
be deleted.
