Day 1, Stop 1
The meter-high outcrop at the semiprimitive
campsite contains two different bedding planes,
both oriented N22W/11NE. The top bed consists of
a very coarse-grained, highly lithified
metamorphosed sandstone with conglomeratic clasts
towards the top, approximately 80 cm thick. The
bottom bed is a medium-to-coarse-grained
sandstone, and is less indurated than the top
The top bedding plane contains elongated,
foliated pebbles, composed primarily of quartz.
Foliation is a preferred orientation of crystal
planes in mineral grains. These pebbles are
oriented perpendicularly to the direction of
maximum shortening (N12E/31SE) of an overturned
fold. The foliation of the minerals dips more
than the bedding plane, in the same direction,
indicating that the outcrop is part of the upper
limb of a fold.
The orientation of the fold is consistent with
the regional Paleozoic stress directions,
demonstrated by the elongation of the pebbles in
The white grains shown here are the foliated
inclusions on the top of the outcrop.
Evidence of a steep
fault on the north side of the outcrop was left
by chattermarks. Chattermarks are minerals
deposited between fault blocks as they move.
Faults leave other indicators on fault surfaces,
such as striae (scratched lines) and fault gouge
(ground-up powdered rock formed when two rocks
slide past each other).
Plumose structures, ridgelike tracing in a
plumelike pattern on the surface of a master
joint, also appeared on the north face of the
outcrop. These may have formed when the rock
jointed before the fault slid.