U-Dig Fossils

This is a working quarry on forty acres of the House Range, and the arrangement is simple: you book a session, they lend you a hammer and a bucket, and what you split out is yours to take home.

The rock does much of the work. The fossil-bearing layer is a limestone shale that cleaves into flat sheets, and the trilobites lie almost flat along those splitting planes, so a tap in the right place opens a slab like a book with an animal printed inside. Staff run an excavator over the quarry regularly to strip overburden and expose fresh fossiliferous rock, so the yield holds up. They reckon an average visitor finds ten to twenty trilobites in four hours.

The unit is the Wheeler Shale, middle Cambrian, around 507 million years old, and it is famous for one animal above all: Elrathia kingii, abundant enough in places that the deposit is classed as a concentration-lagerstatte. The Wheeler has a rarer second reputation too. Soft-bodied animals turn up in it as carbonaceous films, among them Naraoia, Wiwaxia and Hallucigenia, the same strange cast that made the Burgess Shale famous. Work by Robert Gaines and colleagues found the two are effectively segregated: soft-bodied fauna and the Elrathia-rich beds occupy mutually exclusive biofacies, so the layer that fills a bucket with trilobites is not the layer that gives up a Hallucigenia. Together with the Marjum and lower Weeks formations, the Wheeler makes up 490 to 610 metres of one of the thickest and best exposed middle Cambrian sequences in North America.

Go prepared. The quarry sits at about 6,550 feet in the high Utah desert, in the foothills south of Swasey Peak near Antelope Springs, 52 miles west of Delta and a long way from the nearest food or fuel. Bring gloves, safety glasses and plenty of water, and bring your own boxes to carry fossils home in, because the loaned buckets stay at the quarry. July and August highs run 90 to 100.