I checked my old '65 Geology book (I'm stratigraphic in the Gulf only) 
and found a paragraph
that helps link this.

This was the time when trees were there and swamps and ocean streamed 
from the West
and ended up into central Utah and Western Wyoming.  Petrified wood came 
from these trees.
"Clams and brachiopods are present but generally not important." (what 
written by a 'Rex' guy! ?)
Lots of swamps and ferns and clams...

Thanks for the trip.  It turned out interesting getting into a 50 year 
old book of mine.

Martin

On 1/7/2016 7:33 PM, [log in to unmask] wrote:
> ASU has just received this lovely fossil snail from Fred Skillman, an amateur entomologist who found it in a wash on private land near Delicate Arch, Arches National Park, Utah. It is such a treasure for me because it actually has what appears to be fossilized animal and an operculum which became separated when he was cleaning off caked-on dirt. I just had to share with all of you. We think it may date back to the Jurassic.
>
> To see 5 photos just copy and paste the following link onto your search engine.
>
> https://drive.google.com/drive/folders/0B-Vz8pRKgeC8M1NLa1k4U2VZNDg=============
>
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