Colorado, east of the front range, not up in the mtns. The pics above are mostly all from the same septarian nodule. I also find amazonite, few types of Petrified wood, Nice clear and smoky quartz, "agates", fossils, concretions/septarians and other fun stuff in el paso county.
To mount pieces like that I just used a high temp hot glue gun with a hard glue. Its suppose to be removable, I may have even gotten the idea from this site? Most people use acrylic squares but it was a little pricy for me so I got some tile from the homedepot/lowes and made my own.