That would be awesome. I'm contemplated it a few times, but never made it.
In the middle of absolutely nowhere Utah (about 50 miles west of Delta, UT), you can dig for Trilobites. There are commercial quarries (where the remove the overburden, and provide some education and guidance), and there are public quarries on BLM land.
WRT commercial quarries, I've dug at U-Dig Fossils, and at New Dig (which I think was recently bought out, and is operating under a different name). These two quarries are within something like a 1/2 mile of each other, and they're surrounded by BLM land where you can camp for free. There are wild horses in the area too.
[EDIT: there are a number of commercial opal quarries in northern Nevada, but if I understand it correctly, opal must be carefully dried or it completely cracks]
SMB-less as of 02/04/2012. Our savings account is richer, but our adventures are poorer.