Sunday, January 23, 2011

On And Off The Trail–Day Three

Day Three of last week’s winter getaway in Laughlin NV was billed as “Another Surprise Exploratory Hike.” It was certainly a surprise to me because, once again, I had no idea where we were going. The pleasant surprise was that this time the hike leader did.
 
We drove east out of Laughlin on highway 68 to the optimistically named Golden Valley. After a moment of panic regarding the location of our landmark Maverick store, we turned south and then west into the Black Mountains. Cruising southwest of Kingman in a locality I later discovered to be Sacramento Valley, I found it very bizarre to come across a grid of incredibly well marked dirt roads in such a sparsely populated area. Was someone expecting an enormous influx of residents into this desert quarter of northwest Arizona? Situated somewhere between Kingman and the casinos of Laughlin, it wasn’t very close to either but the infrastructure seemed ready for something. 
 
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End of the road, Black Mountains, NW AZ


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Some serious arm-waving by the hike leader


  The geology of the Black Mountains was discussed, as best I could without a geological map in sight, in my previous post.   These are all Tertiary (65-2.6 million years) volcanics (see previous post for Harris 1998) of various tuffs, flows, and breccias.
 
Most remarkable about the hike today were the massive cliffs of lithic tuff (compacted volcanic ash consisting mostly of crystalline rock fragments) that towered all around us as we hiked through our nameless canyon. They were ginormous!  It makes me wonder how much ash was actually thrown out of these volcanoes, how long each particular explosion lasted, and how far each layer can be traced on the ground.
 
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Massive cliffs of lithic tuff in Black Mountains, NW AZ


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Hikers admiring the tuff


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Hikers in the tuff

 
 Back in a canyon the more adventurous in the group (ok, everyone except me) dropped down a steep ravine to view some petroglyphs.

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Dropping down with ropes and ladders

 Since ropes and ladders were involved, I considered my options and chose to stay on top.  I roamed here and there, ate some lunch, and investigated at my leisure the nearby geology.  Again, I do not know the names of the individual volcanic layers; there would be many fine distinctions between them, often depending on the percentage of one or another mineral (silica, in particular) in their compositions, and how explosive each particular volcanic eruption might have been.

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Massive cliffs of lithic tuff, Black Mountains, NW AZ



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Plagioclase clast with darker biotite and possibly pyroxene or hornblende


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Boulders (not basalt) from cliff layers litter the hillside

 

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Boulder with opal (hydrous silica) on fracture surface


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Opal (hydrous silica) on fracture surface of boulder

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Boulder layer above
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Boulder layer above
                                                          
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Later afternoon light on cliffs

9 comments:

  1. To bad you didn't have an idea about where you were going to do a little pre-research. But then it is fun to play geo detective, especially in such an interesting landscape. Finding the opal layer is cool. Excellent captures.

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  2. A very interesting undertaking: leading a field trip to an unknown place!

    That one close-up photo of the ash-flow tuff shows some nice lithic fragments, dark ones, maybe basalt?

    Here's a link to the general volcanic history of AZ, although it doesn't show anything particular about the Black Mts.

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  3. Thanks for your comments, Silver Fox, and also the link to AZ volcanics, which I have saved to read. This was such an interesting area, but I was with hikers and not geologists so there was no discussion as to what was what. I was pretty much on my own! The tuffs were absolutely amazing - I thought the dark crystals might be hornblende or pyroxene, and biotite. Thin sections would certainly be nice! They could have been minute basalt fragments, though.

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  4. I was thinking of those relatively large subangular, subrounded fragments in the lower part of your 4th photo.

    The dark xtls in your close-up look like they could easily include both biotite and hornblende.

    I love volcanic rocks! :)

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  5. Silver Fox - Thanks for the clarification of which photo you meant! Unfortunately I didn't take a really good look at those fragments (had to keep up with those hikers, after all) - I thought they might be country rock brought up in the explosion. Could be basaltic, however... fragments from a flow already on the ground? My thought at the time was "fining upward?" I did see what I thought was a basalt flow, up off in the distance in some cliffs above where we were hiking.

    I become more intrigued with volcanics the more I see them.

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  6. Too bad you didn't go down into Dripping Springs itself in the canyon and then on down to the lower level where the petroglyphs are. It is worth the trip. The last time I was in the Blacks in that canyon was 7-15-1980. There is a very small spring where they climbed down into, hence the name "Dripping Springs."

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    1. Thanks for your comment, Eddie. It would have been nice to have seen the springs, but if I had gone down to see the petroglyphs I would have missed my investigation of all these intriguing volcanic rocks. I had to choose one over the other. Plus, I'm not a big fan of ropes and ladders of unknown age and stability!

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  7. In 1980 you climbed down a tree to get to the lower level. I have noticed that in a hike that Mohave County Search & Rescue did in 2014 they repelled in. Either way, it is worth going down in there. And as an aside, in one trip my friends Dan and Keith and I did prior to 1980, we climbed up onto that legde shown in the poto you titled "massive cliffs." I went to the right, (north) side of that ledge as far as it extends and found a very old wooden trunk with one leather shoe in it. I wonder if it is still there.

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    1. Hi Eddie - Very cool to find that trunk and shoe. I wonder what else is out there that will may never be found! It is such an interesting area.

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