Thursday, November 7, 2013


An example of the Trilobites we found.
The trailer sagged and the lights shown downward onto the ground as we pulled out of Delta, Utah, on the last leg of the journey to Quartzsite.   The car was full of them, the back of the van was full of them.   And the buckets that wouldn’t fit in either the car or the van were stuffed into the back of the trailer so precariously that an avalanche would occur if we opened the door again.    We pulled into Delta, Utah several days before, intending only to change a tire, grab some lunch, and then get back on the road.   But then the Trilobites happened.  

Looking around at the seeming “nothingness” of Delta, I had casually mentioned that the desert in this part of Utah was chock full of fossils.   Trilobites, to be exact, the ancient ancestors of today’s lobsters and crabs.   Enough said.   We were off to find some of these little prehistoric sea creatures for ourselves.    Three days and many aching muscles later we had more trilobites than we had places to put them.   

Artist's rendering of Trilobites
Trilobites are members of the phylum Arthropoda, which includes modern animals such as insects, spiders, scorpions, ticks, crabs, lobsters, and centipedes.  They belong to an extinct class of marine organisms called Trilobita which means three-parts, and refers to the three segments of the trilobite’s exoskeleton.   More than 500 different Trilobite species have been found in a band of Cambrian Period limestone, siltstone, and shale that extends across the Northwestern portion of Utah.    During that time period, about 550 million years ago, western Utah was covered by a shallow sea with slow moving rivers carrying sandy sediments into it.   The land we now refer to as Utah was located closer to the equator at that time, and the water in this shallow sea was warm.   It was in this warm, shallow, and nutrient-rich water that the Trilobites lived, crawling on the bottom while scavenging or grabbing passing prey. 

The Wheeler Shale in the mountains of the House Range in Millard County is known as one of the top collecting locations for Trilobites in all of Utah.    Here, the Trilobites are located in a 15 feet thick layer of shale and mudstone throughout the mountains southwest of Delta.    We dug in several locations, and found two that produced quite prolific concentrations of Trilobites.   One of the locations was a light gray and reddish mudstone, and the other was a dark gray shale.   We found about 5 different species of Trilobites over a two day period.    We found both full trilobites and imprints in both locations, as well as plates and partials.    Other fossils found with trilobites include crinoid stems and spiral-shelled animals similar to ammonites. 

Trilobites are found by splitting the layers of the rock.   In the mudstone layers, the rocks split somewhat easier, but they are also softer and more fragile.   In this location we found the fossiliferous layer about 5 feet beneath the surface of the foothills of the mountains.   We dug out slabs of mudstone and split it with the rock hammer or a chisel.    Many times the split along the cleavage would reveal the Trilobites, but other times the split would damage them or only reveal them partway.   The mudstone Trilobites break more easily, so it is important to use a little more care when removing layers of rock from the mudstone deposits.   We also found trilobite imprints in the tailings while walking around the collecting areas.

U-Dig Site, Delta, Utah
In the harder dark gray shale, the work was more difficult.    Here we used pry bars to lift up sections of the shale layers, and then used a maul to break the sections into smaller, more manageable pieces that we could then split with the rock hammer and chisel.   The positive side of the harder shale is that the Trilobites are less delicate, however, it is also more difficult to control the break so many of the Trilobites were only partially exposed or broken.   We also found fossils which had a calcium layer of the exoskeleton intact, but it was very brittle and disintegrated when exposed.  Another plus to the shale, is that often whole trilobites will erode out of the rock and can be found by sifting through the dirt and shards left behind in the pockets from where slabs of rock where removed.    That was a great way to take a break from the heavy work of hard rock mining, yet still be productive in recovering the fossils.  

Though hard physical work, the experience of digging trilobites is a fun and exciting activity the whole family will enjoy.    Older folks and young kids can enjoy finding the loose trilobites in tailings and dirt pockets while the more fit people in the group do the heavy work.   Older kids who can use a rock pick will find themselves content to chip at smaller pieces that are dug out by someone else, or cleaning and sorting fossils dug by their group.   

Mudstone Trilobite Deposit
There are several locations near Delta, Utah, to dig for trilobites.    For less experienced people who want to be assured of finding trilobites, a great experience is the U-Dig Fossil site.   U-Dig is a pay-to-dig location about 35 miles west of Delta.   To reach the site, take Hwy 50 west out of Delta for approximately 15 miles until you see a well maintained gravel road heading off north into the desert.   The road will have a sign saying "U-Dig" with an arrow.   Follow this road and the signs leading to U-Dig through the desert for about 20 miles.   You will be heading into the mountains at the later portion of the road.  At the approach to the U-Dig site you will see gray shale tailings piles, some heavy equipment, and a small gravel parking area off to the right.    The folks at U-Dig are friendly and knowledgeable.   You can use their buckets and rock picks, or use your own tools.  The staff will show you where to look for the trilobites and will start your group out by breaking out a section to begin working on.  For more information on U-Dig go to their website.    

Antelope Spring
If you don't want to go to a pay-to-dig site, there is a nice mudstone site that we found which produced nice trilobites.   To get to this location, take the road to U-Dig about 12 miles to the junction with the gravel road to Marjum Pass.   The junction is marked by a Spring called Antelope Springs, which is underground, but has a pipe and faucet inserted into it.    The water flows out of the faucet into a narrow gully that has been dug to carry the water to a cattle watering station just to the left of the road.  Turn left at Antelope Spring onto the road to Marjum Pass.   Travel down that road for about 6 miles.  Just before getting into the mountains you will see diggings along the side of the road, a pit and a wash, and tailings piles.
  A few hours in this location should produce several of the mudstone trilobites.

It is a good idea to check other areas like washes and gullies, or even canyons where shale layers are exposed.  We found one nice trilobite imprint near a canyon, but there didn't seem to be very many at that location, or they were not very easy to find.    It is possible we didn't look long enough to find the layer that contained them.   Another area where we looked, unsuccessfully, was a dig site called "The Community Dig".   There are lots of exposed layers of shale there, but after sampling in several places, we found no sign of trilobites or any other fossils in the
exposed rock or any tailings.

We are open in Quartzsite so you can come by to see and purchase Trilobites that we collected, or get books, maps and everything you need to go out and have some exciting prospecting adventures of your own here or elsewhere.    We are open 7 days a week from 10am to 6:30pm, at A37 Rice Ranch in Quartzsite, 605-376-8754, and 24/7 at

U-Dig Site Outside of Delta, Utah