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.
|End of the road, Black Mountains, NW AZ|
|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.
|Massive cliffs of lithic tuff in Black Mountains, NW AZ|
|Hikers admiring the tuff|
|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.
|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.
|Massive cliffs of lithic tuff, Black Mountains, NW AZ|
|Plagioclase clast with darker biotite and possibly pyroxene or hornblende|
|Boulders (not basalt) from cliff layers litter the hillside|
|Boulder with opal (hydrous silica) on fracture surface|
|Opal (hydrous silica) on fracture surface of boulder|
|Boulder layer above|
|Boulder layer above|
|Later afternoon light on cliffs|