That noise you hear is coming from my knees.


Saturday, February 11, 2017

Fossil Shell from San Dimas

While hiking a couple of weeks ago, Queen D noticed an unusual looking rock along one of the dirt roads that we hike and bike on at Bonelli Park.




Of course, a discovery like this sent me on the interwebs researching to find out what it is.  We’ve hiked there quite a bit and have never seen anything fossil-related, although now we’re probably going to pay much closer attention.  Here’s what I’ve found:

Dr. Jonathan Nourse is a faculty member at Cal Poly Pomona who has done some work in the area.  One of his students did a senior thesis and mapped the conglomerate outcrops in exactly the area where the item was found.  Based on the information posted on Dr. Nourse’s website, and a search of shell fossils from the nearby area, I’ve narrowed it down to the following:  it’s an Ark Clam (Family – Arcidae) from the Puente Formation, a member of the Monterey Group of marine sedimentary rocks, deposited during the Miocene epoch, 11 to 15 million years ago.


I’m not sure about removing such specimens from the park – it’s part of the LA County park system.  If they want it back, I’m happy to oblige.

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