How did Spanish explorers mark rivers and waterways leading to treasure?

[Old Dirtbag]

I have noticed an odd stone structure/natural formation at the forks of where two rivers meet. I have not been able to look at it up close, but it is looks like one of those standing stones or "dolmens" at Stonehenge.

Is there any possibility that it was placed there as a marker by the Spanish? If it is manmade, what symbols should I look for? The Spanish were definately in the area during their reign.

 

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[Tom_in_CA]

even if manmade , most likely modern (post Spanish), & having nothing to do with treasure .