Trilobites.info has a page about the trilobites of the Wheeler Shale in Utah.  The Wheeler Shale dates to the Middle Cambrian, about 505 million years ago.  The formation is known for a diverse group of soft bodied animals, many of which are the same taxa found in the Burgess Shale (508 million years ago).

It is notable that the trilobite fauna of the Wheeler Shale, being a Middle Cambrian locality, is dominated by Ptychopariida, Corynexochida, and Agnostida. In addition to trilobites, there were other species of arachnomorph (trilobite-like clade) arthropods such as Naraoia. These trilobite-like arthropods demonstrate that the group from which trilobites arose was itself successful and diverse, though being uncalcified, are only preserved under exceptional conditions, such as at exceptional lagerstätten such as the Burgess Shale and Chengjiang. Because the Burgess Shale was the first lagerstätte with such exceptional preservation, other sites with similar preservation are referred to as “Burgess Shale type” lagerstätten. This level of preservation occurs only infrequently in the Wheeler Shale.

The most famous trilobite found in the Wheeler Shale is Elrathia kingi.  They have been collected in the millions and has been sold all over the world.  If you have bought or seen a trilobite, the chances are very high it was an Elrathia kingi.  Actually, the Wheeler Shale is home to about fifteen different genera of trilobites.  Other fossils that can be find there include brachiopods, jellyfish, mollusks, worms, and echinodems.

If you go to Utah, you can visit U-Dig and collect your own trilobites.  Delta is a little more than 100 miles south of Salt Lake City in western Utah. You can also order U-Dig Shale to be mailed to you here!