H28:
SE-NW anomaly, crossing Hf,
S20 T41S R12W & S24 T41S R13W (10/25/06)
Access and Purpose
The Geology of this area is shown on the Pintura Quadrangle.
Additional information about the PVM intrusions is available in a
publication of the Utah Geological Survey (UGS): Survey
Notes,
September 2, 2002,
Volume 34, Number 3, "Massive Gravity Slides Show Value of Detailed
Mapping" by Grant Willis.
Discussion
The major objection to the location of the fissures (as
an indication of a regional fracture) is that of its emplacement just
above the Virgin River, indicating that the
fissures result from gravity spalling and potential rotation of the
cliffs into the Virgin River. This would be
acceptable, except for the observation that the fissures continue where
the river has taken a turn perpendicularly to the fissure orientation.
Also, the fact that the river has found the fissures below its path (as
indicated by the water sinking into the subsurface, due to the
additional head of water behind the diversion dame) confirms that the
fissures were there before the river found the fracture path. The paths
of the river are in two major directions NW-SE and NE-SW, suggesting
that the river found the pre-existing fracture weaknesses as an easy
outlet, getting through the lip of the Kaibab sediments, which dip up to
the west- creating a barrier for the early river.
There is a saddle to the SSE of the river, in the hills
toward Apple Valley- which
would indicate that the fracture system continues in that direction, but
this feature has not been investigated.
On the other end of the perceived fracture system, the
hikers traced the path of the Wet Sandy (a signed trail), as far as the
first outcrop of sedimentary rock. The creek is filled with PVM boulders
east of this point, and no information is gleaned from this portion. The
fracture system portrayed in the stream borders indicates that the
Mesozoic sediments have been faulted against the intrusive rocks, with
faults trending mostly NE-SW- the trend of the PVM. Faulting to the east
in Tertiary rocks is mostly N-S, similar to the outcropping of the
Jurassic rocks to the west.
Illustrations
