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]

Quote: Originally posted by geoffff

Somewhere within 20k of San Evaristo?

Quote: Originally posted by baja-chris

Up a wash from the dump north of Loreto?

Where?

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

Well then, it's gotta be Calamajué Canyon.

Quote: Originally posted by TacoFeliz

Well then, it's gotta be Calamajué Canyon.

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?

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): I am too lazy to go through the vivabaja link you shared where's this?

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.

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!

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?

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...

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).

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

Quote: Originally posted by bajaric

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!