[BR-Crater] objective of Crater Assault 4

[Ian Kluft]

We'll be hitting the road tomorrow for the Crater Assault 4 trip.  It will
be my 40th trip to the Black Rock Desert.

There have been a bunch of messages about the planning for the trip.
Though it's been posted before, here's a review of the background info
on the objective behind this trip, from the crater research perspective.
(For Stratofox, it's also a new-member training opportunity.)

We'll be hiking in the area of Pahsupp Mountain, a place we have not
explored before at Black Rock.  In the general scheme of things in the
Black Rock region, Pahsupp Mountain has been just a 5000' elevation peak
that you drive by on Jungo Road without a reason to give it a second look.
It's located south of the railroad tracks near the Cholona playa entrance.
Several things we've learned in recent months point there as an educated
guess for another place we should explore in the impact crater research.

First, there's the updated estimate of the outline of the impact structure
from a 30x40 mile ellipse to a 54 mile circle, which I posted in January.
The center of the area was moved with that estimate.  So Pahsupp Mountain
is about the same distance from the center of the area as the southern
Black Rock Range which we've explored quite a bit already.

Second was some advice from geologist Bob Verish about where to focus our
search for shatter cones.  In an impact, shatter cones are only formed
underground.  So if any are to be found, we'd have to expect to find them
in places where erosion and/or uplift have exposed them at the surface.

There is an apparent north-south fault line along the east side of Pahsupp
Mountain.  That's where the route of Sunday's hike will focus, where it
looks like there has been fault uplift.  So the guess is we should get a
look at some deeper rocks there.  It isn't a long route, which is intended
to give us time to explore.

In the southern Black Rock Range, we've found rock formations up to 2 miles
apart which have some resemblance to shatter cones, but not good enough in
quality.  In order to double check whether that was a useful observation or
a wild goose chase, I traveled last September to Santa Fe NM to compare with
a confirmed impact site.  Along NM Hwy 475 northeast of Santa Fe in the
Sangre de Cristo Mountains, about a mile before the entrance of Hyde
Memorial State Park, the road winds through a canyon with nearly a mile of
rocks riddled with shatter cones.  (Along a road built in the 1920's, they
were recognized/discovered in 2005 and published in 2007.)  Indeed outside
the area of the good quality shatter cones, I observed there are patterns of
"uncountable apexes" in the rocks similar to what we've seen at Black Rock.
So that continues to encourage us to keep searching at Black Rock.

There are sample images of shatter cones at
   http://en.wikipedia.org/wiki/Shatter_cones
   http://ian.kluft.com/pics/nm-200809/
   http://www.impact-structures.com/shattercone/shatterconepage.html

Having never stopped at Pahsupp Mountain before, we really don't know what
to expect.  So we're not setting much in the way of specific expectations.
We have this idea that it should be a good place to look - and we're going
to test that idea.  We'll look around, familiarize and just find out what's
there.  We'll bring back pictures.