Sally sells Seashells...in the desert?

We found some wonderful treasures in the desert recently.  Where there is water, apparently there are bottom feeders. Or in this case, where there was water.  Since there is most definitely not any there now.  Next to some coyote tracks and cactus we found these beauties:

 

Apparently its not too uncommon, even though with all our hiking we have never come across them before. I am thinking if we find enough for a craft I might have the kids decorate a picture frame with them. Although its perfect for our oldest as she happens to collect sea shells.  Not too great for bringing home inside of pockets though.  Like my daughter said, "I don't like having sand in my shorts."