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David K
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Somewhere in Baja
4x4abc, (or under his real name, over on Facebook), has been posting random photos with this title "Somewhere in Baja" just for viewing enjoyment.
Borrowing on that theme, here is 'somewhere in Baja' (guesses welcome):
[Edited on 6-27-2024 by David K]
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geoffff
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Somewhere within 20k of San Evaristo?
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David K
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No, further north.
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baja-chris
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Up a wash from the dump north of Loreto?
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David K
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Nope, further north.
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David K
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Where?
The answer is in this trip page: https://vivabaja.com/p916/
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4x4abc
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Mood: happy - always
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my "somewhere in Baja." posts were not intended to be a question about the location
it is just a photo dump of the many beautiful Baja places I have been to
a way to share pictures that I have not been able to use in publications etc
a memory lane trip
but i am happy that so many of you recognize the spots and post names
what I find interesting is the varying responses on different facebook sites
on some I get many views and very few comments
on some I get a moderate number of views and many comments
Harald Pietschmann
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David K
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Quote: Originally posted by 4x4abc  | my "somewhere in Baja." posts were not intended to be a question about the location
it is just a photo dump of the many beautiful Baja places I have been to
a way to share pictures that I have not been able to use in publications etc
a memory lane trip
but i am happy that so many of you recognize the spots and post names
what I find interesting is the varying responses on different facebook sites
on some I get many views and very few comments
on some I get a moderate number of views and many comments
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Yes, pretty interesting! All people are different and think differently but in our sphere, all love Baja California!
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TacoFeliz
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Well then, it's gotta be Calamajué Canyon. 
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David K
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Hi Jay,
Nope, too far north... but on that web page, just continue on and see the photo after we ate at Mark, Olivia, and Nathan's Playa Buenaventura Cantina.
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mrbogo
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| Quote: Originally posted by David K | 4x4abc, (or under his real name, over on Facebook), has been posting random photos with this title "Somewhere in Baja" just for viewing enjoyment.
Borrowing on that theme, here is 'somewhere in Baja' (guesses welcome):
[Edited on 6-27-2024 by David K] |
I am too lazy to go through the vivabaja link you shared where's this?
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David K
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| Quote: Originally posted by mrbogo | | Quote: Originally posted by David K | 4x4abc, (or under his real name, over on Facebook), has been posting random photos with this title "Somewhere in Baja" just for viewing enjoyment.
Borrowing on that theme, here is 'somewhere in Baja' (guesses welcome):
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I am too lazy to go through the vivabaja link you shared where's this?
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It is abouth halfway down from the top of that trip page, on the same page: https://vivabaja.com/916/
Look, and learn the answer.   
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bajaric
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Side canyon on the road out towards the manganese mine at the end of the Bahia Concepcion peninsula.
So, looking at that vein of white rock, it appears to be a "dike". Dikes are formed when a hot solution of minerals invades a fracture in the "host
rock" and then crystallizes into a new rock, forming a vein in the old rock.
"Pegmatite dikes" in eastern San Diego County and the Sierra Juarez are known to contain some exotic gemstones, including tourmaline, my favorite.
Some guys out in east county mucked out an old tourmaline mine a couple of decades back and after digging a little further into the old mine made a
big strike that yielded a huge payday in tourmaline gems.
What is weird is that this dyke appears to be in soft sedimentary material, not in a hard host rock. The only thing I can think of is that there is a
layer of host rock towards the bottom that decomposed, leaving the dike sticking up in the air, then a new layer of sediments was deposited around it.
Any geologists on here can explain what is going on here?
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David K
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Thanks Rik. We ended up in this dead-end canyon (Arroyo Tres Marías) when we took the wrong fork trying to go to the petroglyphs (Arroyo Los
Pintados). The remains of some ranch (?) was in there at the end of the road, oddly built in the arroyo.
I think I spotted this dike on satellite imagery, here: 26.6451, -111.6883
I know a geologist and will ask him to explain, but you did very good!
I also hope your excellent book is doing well!
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Maderita
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| Quote: Originally posted by bajaric | Side canyon on the road out towards the manganese mine at the end of the Bahia Concepcion peninsula.
So, looking at that vein of white rock, it appears to be a "dike". Dikes are formed when a hot solution of minerals invades a fracture in the "host
rock" and then crystallizes into a new rock, forming a vein in the old rock.
"Pegmatite dikes" in eastern San Diego County and the Sierra Juarez are known to contain some exotic gemstones, including tourmaline, my favorite.
Some guys out in east county mucked out an old tourmaline mine a couple of decades back and after digging a little further into the old mine made a
big strike that yielded a huge payday in tourmaline gems.
What is weird is that this dyke appears to be in soft sedimentary material, not in a hard host rock. The only thing I can think of is that there is a
layer of host rock towards the bottom that decomposed, leaving the dike sticking up in the air, then a new layer of sediments was deposited around it.
Any geologists on here can explain what is going on here? |
That definitely seems unusual for a dike. My knowledge of geology is limited to 3 or 4 undergrad courses in the 1970s. I haven't been in that area, so
I'm certainly not arguing your observation.
Upon seeing the photo, my immediate, gut impression was that I was looking at an area created by volcanism. Could the layers of "sedimentary"
deposition that we see actually be layers of volcaniclastic deposition, consisting of compacted, but poorly cemented, rock and ash? With an extrusive
igneous, silica-rich (light color) volcanic plug. Such as, a rhyolite plug on a cinder cone vent. Then the cinder cone's weak rock easily eroded to
expose the rhyolite plug. Just wondering...
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Maderita
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David, thanks for posting the GPS coordinates. I was able to look it up on Google Earth to locate the area.
I was then able to find a map of the geology, which includes the eastern side of Bahía Concepción.
The map indicates: "(4) post-Comondú basalts and basaltic andesites"
Bahía Concepción area. Geological map showing location of the hydrothermal vents and intertidal springs. (1) Alluvial deposits; (2) volcanic rocks:
basalts, dacites and rhyolites; (3) marine sedimentary rocks; (4) post-Comondú basalts and basaltic andesites; (5, 6) Comondu Group: volcanic and
volcano-sedimentary continental rocks; (7) Comondu Group: marine deposits; (8) hydrothermal springs and vent sites (after Bustamante-García, 1999;
Ledesma-Vázquez and Johnson, 2001; Rodríguez-Díaz et al., 2010).
https://www.researchgate.net/figure/Bahia-Concepcion-area-Ge...
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David K
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Thanks John for that information!
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David K
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From my geoplogist friend [double spacing added for easier reading]
David K, if I have located the intrusive dike shown in your photo correctly, and I believe that I have based on your coordinates, then your friend in
in error about the geology- it is not soft sedimentary rock at all.
The bedrock unit is the Miocene Pelones formation, a 2000 meter thick basal unit of the Comondu Group of Oligocene and Miocene volcanic rocks. The
Pelones fm. consists of volcanic agglomerates, basalt flows, and tuffs with occasional relatively thin interbeds of conglomerate and tuffaceous
cross-bedded sandstone.
Sometimes thick sequences of volcanic flows can appear to be layered sedimentary rock to the novice, but upon examination in the field one can more
readily identify the volcanic nature of the bedrock. The Pelones formation is intruded by a number of gabbro stocks and dikes, but in several areas
such as the area in question, the Pelones is intruded by several tonalite stocks and dikes.
Tonalite is felsic (light colored) intrusive rock as indicated by the light colored dike in your photo which appears to be nearly white. Upon closer
examination you would probably see that it is speckled with biotite and other mafic minerals. Tonalite is somewhat similar to granite in composition
with respect to quartz content, but the big difference being that the feldspar in tonalite is 90% plagioclase, whereas, granite contains orthoclase
(alkali feldspar).
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David K
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More...
David K, In this oblique aerial image of the area in question, you can see the same tonalite dike in your photo from a different angle. You can also
see that the Pelones fm throughout the flank of the canyon is "shot through" with tonalite dikes (my red arrows). I might also mention that manganese
mine at northeasterly end of the Sierra Los Gavilanes peninsula, about 15 miles NE of your photo is related to hydrothermal mineralization of the same
Pelones formation!
Hope this answers your gold prospecting friend's concerns, please pass it along that the tonalite dike intrudes primarily volcanic bedrock, and not
soft sediments in this case. Someday I would like the opportunity to meet him an to do some gold prospecting in Baja with him. Any reason for a trip
to Mexico is a good enough reason in my book! Saludos amigo
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bajaric
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Ahhhh, the old tonalite intrusion into volcanic agglomerates trick! Ha Ha. Somehow the layers of Oligocene host rocks that appeared to me to be
recent alluvial material managed to stay horizontal for about 15-20 million years. Impressive!
I have not been down to Baja California for a couple of years. Have been thinking about doing a trip to go look at some of the old mining areas and
poke around a little. I got an "e bike" and am thinking of taking a couple of weeks to travel all the way from the border down to the Vizcaino
desert, mostly staying at paid campgrounds or motels, and do some rides on the e bike along the way. When the plans get a little firmer will post an
itinerary to see if your friend or anyone else might like to join up for a portion of the trip. I don't mind going by myself, but sometimes it is
nice to have some other people along for company and in case something goes wrong.
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