[BR-Crater] initial report from Upper High Dry visit

[Ian Kluft]

I went to Upper High Dry lakebed for a few hours on Sunday morning.
Here's a quick initial report.  I'll send more after I post photos
this evening.  But that will only go to the br-crater mail list.
So subscribe to br-crater if you want to follow this discussion.
   http://www.thunder.net/mailman/listinfo/br-crater

Hiking arrangements
-------------------

We ended up only going in one vehicle, though with "radio following" by
Paul Hopkins KE6DAX from the AeroPAC flight line.  Though there had been
responses on the AeroPAC list with people interested in coming along,
everyone else bailed out...
* Charlie Wittman's camping fridge exploded enroute to Black Rock, covering
  his camping gear in ammonia and forcing him to turn back to clean it up.
  Word that he passed along is he's interested and wants to see the place.
  (Charlie is an engineering geologist with impact crater experience.)
* Seth Wallace wanted to see Upper High Dry but was on the fence about
  whether he could leave his wife watching the kids alone all morning.
  He decided to take a rain check and join us if we do a similiar trip
  in September at XPRS, when he'll be there alone.
* John and Donna Ballard expressed interest.  But it appears they didn't
  make it to Aeronaut.

Given the level of interest, we'll do this again in the future.

Paul and I talked about what safety margin I'd have going in one vehicle.
We thought his temporary Amateur Radio simplex repeater (record and replay
operation) on Cassidy Ridge (near the Steamboat) should reach pretty well
to Upper High Dry, and it did.  So we just checked in with him regularly.
I wasn't hiking alone - my co-worker Joe Isca came along.  Also, Paul
knows that area and could reach it quickly if we didn't check in.

We set noon as the time that they'd come looking for us if they hadn't
heard any reports and we weren't back at the launch site.  But we did
provide regular radio check-ins.

I arranged with Paul that I'd park the truck at the edge of Upper High Dry
lakebed pointing the direction we were going hiking.

Hike at Upper High Dry
----------------------

As seems to be the norm for our visits there, we found nothing definitive.
But also normal for each visit, we did find interesting and encouraging info.

We briefly stopped at the top of the island on Upper High Dry before 8AM.
It started to rain (from a small trough line crossing Black Rock in the
morning) so we got off the hill as a precaution from lightning.  The trough
passed quickly.

The obvious first point to hike was where I had proposed on the map, east
of the lakebed.  I quickly figured out from the loose rocks on the way up
there, and just looking at it, that this ridge was too high in the rock
layering for what we were looking for.  The rocks were all lava-like
(possible impact melt) or breccias (jumbles of different rocks), which
would all be formed post-impact.  The photos hadn't been good enough to
tell that.  We turned back before getting up to the ridge.  If there were
any shatter cones to find, they'd be in pre-impact rocks.

A look around the lakebed showed the melt and breccia layers on top of a
curved group of rocks that didn't look like melt at the north side of
Upper High Dry.  I pointed the truck in the direction of the hike - and
we didn't leave sight of it as we checked two outcrops on the way up.

The first outcrop had vertical-fractured rocks with white breccia dikes
(vertical jumbled fill) in it.  So far so good.

As we climbed to the second outcrop, the parallel fractured rocks got finer
grained until some unbroken ones stuck up almost like knives.  Fortunately
there weren't many of those.  The fractured rock seemed to face straight up
until we got to the top of the first small ridge and had a closer look.
Some fractures seemed to be nearly perpendicular to each other, or other
angles.  My observation of the pattern was that they were all around an axis
pointing slightly up and ESE.  Joe agreed it looked like that was the only
commonality between these otherwise chaotic-looking different sets of
parallel fractures in the rocks.

We checked a nearby area where the rock color changed from orange to gray.
These different rocks had the exact same fracturing pattern, which is also
encouraging.  Also in this set we found some possible branching fractures
which we brought back for a closer look.  I don't know if they're shatter
cones.  But I'm certain they're not the textbook quality look that reviewers
of the web site have wanted to see.

Post-trip analysis (so far)
---------------------------

I had already identified in January that the different sets of parallel
fracturing of the rocks on the island in the Upper High Dry lakebed are
about an axis pointing upward and roughly to the east.

After coming home I lined up the terrain we were looking at in the direction
of the rock fracturing axis, to see where it would point.  The map confirmed
my suspicion that it would point directly toward the center of the semi-circle
in the southeast hook of the Black Rock Range, which is already identified
as the center of the theorized crater.

I showed the photos of the rocks to Brad over a late dinner.  He was
surprised.  He says he's never seen a fracturing pattern like that in
person or described in any geological paper he recalls.  He considered it
encouraging that they appear to fracture around an axis pointing up and
toward the theorized center, which is where shatter cones are known to
point as well.

We agreed that the next step in testing this idea needs to be to check a
different part of the Black Rock Range near there where one would expect a
bearing about 90 degrees off from the bearing of the fracture axis found
on Sunday.  That should be in the Black Rock Range south or southeast of
Upper High Dry Lakebed, or in the hooked southeast point of the range
itself, wherever we can find rocks which appear that they'd be from
pre-impact layers.

There isn't a lot left due to erosion so exactly 90 degrees may not be
possible.  The closer to 90 the better.  We'll just have to look for the
best we can find there.