Ancient Fossil & Mineral Hunt: Utah Rockhounding Road Trip

Mounds Reef: Pelecypods, Cephalopods, Gastropods
Location Coordinates: 39.4649, -110.586
Green River Cutoff Road: Agate, Petrified Wood
Location Coordinates: 39.2, -110.377
Greasewood Draw: Celestite, Jasper
Location Coordinates: 38.852, -110.382
Highway 24: “Devils Toenails” Oyster shell fossils
Location Coordinates: 38.3708, -110.814

You’ll start your adventure in Price, and head southeast on Highway 6/191 towards the Mounds Reef area, south of Sunnyside Junction. Here, you’ll find sandstone concretions containing coiled-up marine fossil specimens up to six inches long. These organisms lived over 80 million years ago when the eastern half of Utah was covered by an inland sea that stretched from the Gulf of Mexico to the Arctic Ocean.

Next, return to the highway and continue south to the Green River Cutoff Road, heading west for nearly four miles. In the hills south of Summerville Wash, you will find red agate and petrified wood. Afterward, rejoin the highway and head south to I-70, then turn onto Highway 24 South toward the Greasewood Draw area to hunt for jasper and geodes filled with pink, white or blue celestite.

From there, follow Highway 24 south to Hanksville, then head west for several miles toward Sand Wash Road. In the hills north of Highway 24, you can find thousands of fossilized oyster shells, colloquially called “Devil’s Toenails.” These oysters (Pycnodonte newberryi) inhabited the same inland sea as your first stop, approximately 90 million years ago.

Where to Stay: Hanksville or the Caineville area’s Cathedral Valley Inn, which is in between Hanksville and Capitol Reef National Park. Nearby Torrey also has additional lodging and dining options.

Tips: Some useful tools and items to bring are a classic rock hammer, safety glasses, spray bottle with water, a vehicle with 4-wheel-drive, sunscreen and twice the amount of drinking water you think you’ll need. (Read: How Much Water to Pack for Your Utah Adventure) Know what land you are on: BLM public land that is not within an active mineral claim allows for reasonable amounts of rock collecting. Collecting of any kind is illegal within national park boundaries.

Swing Arm City: Agate, Jasper, Chert and Petrified Wood
Location Coordinates: 38.3652, -110.914
Caineville Reef: Agate, Jasper
Location Coordinates: 38.4434, -110.9741 (location on Utah Rockhounder web map is a bit too far south)
Sweetwater Creek: Hornblende
Location Coordinates: 38.0882, -110.969
Fremont River: Red Agate, Jasper near Capitol Reef National Park (time permitting)
Location Coordinates: 38.2803, -111.116

Beginning in Hanksville, drive to the Swing Arm City OHV Recreation Area. On both sides of the highway — please be safe if crossing the road and watch for approaching traffic — you can find agates and colorful chert, along with the opportunity to collect petrified wood.

When you are finished there, take either Factory Butte Road or proceed further west onto Cathedral Road, then turn onto Factory Road to reach the Caineville Reef area for more agate and jasper. To reach the greenish-gray Curtis Formation containing the agate and jasper, you will need to hike about a mile west of the Caineville Reef — so be sure to bring plenty of water and sunscreen. Nearby, you will also find seams of gypsum in the Jurassic-age Morrison Formation.

After returning to your vehicle, make your way back to Highway 24 and turn south onto Notom Road. From there, head east on Henry Mountains Road over Wildcat Mesa to the South Creek/Sweetwater Creek area. In the creek's alluvium, you will find diorite boulders and cobbles containing large hornblende crystals. These rocks originated from the massive intrusive body of magma responsible for the uplift of the nearby Henry Mountains.

Head back to Notom Road, and if time permits, park roughly half a mile east of Notom Road on Highway 24 to search for red agate and jasper along both sides of the road and the banks of the Fremont River.

Where to Stay: Torrey or the Caineville area’s Cathedral Valley Inn.

Tips: Timing is critical for visiting these sights — avoid the summer monsoon season if possible. This season, which runs from July through September, brings the highest frequency of flash floods (though they can happen at any time of year, so stay vigilant). The area also features a specific type of clay that makes driving extremely difficult or impossible when wet, even with a capable 4x4. Bottom line: If it’s going to rain — or if you aren’t sure — don’t risk it.

If you want to take a break from rockhounding, you can substitute a collecting site with a visit to the Bentonite Hills, Capitol Reef National Park, Factory Butte or Moonscape Overlook for some world-class sightseeing. (Read: A Day at the Factory)

Sigurd area: Gypsum
Location Coordinates: 38.8276, -111.941
Marysvale Canyon: Bixbyite, Rutile and Amethyst
Location Coordinates: 38.4854, -112.246
Durkey Creek: Zeolites and Agate
Location Coordinates: 38.4631, -112.17
Blackbird Mine: Psilomelane Manganite (time permitting)
Location Coordinates: 38.4243, -112.121

For your final day, start by heading west out of Torrey, Utah, on Highway 24, then northwest through Loa and past Koosharem Reservoir toward the hills near Sigurd to search for gypsum. Once you’re finished here, connect to I-70 West and merge onto Highway 89, following it south toward Marysvale. Right before reaching the south end of Marysvale Canyon, make your second stop to hunt for bixbyite, rutile and amethyst crystals.

For your third site, head south into Marysvale, turn east into the hills and follow Durkey Springs Road along Durkey Creek. This area features volcanic rocks containing zeolite minerals like chabazite, stilbite and mordenite. If you proceed to where the road washes out as it turns southeast, you'll find plenty of agates to pick through.

For your final location of the trip, head southeast to the Blackbird Mine near the mouth of Straight Canyon to hunt for manganite. This distinct mineral forms dark gray to jet-black clusters that look almost like tiny grapes. From here, your next destination is home! If you're heading back to Salt Lake City, it's just over a three-hour drive north. If it's getting late, Richfield and the surrounding towns along I-15 offer plenty of convenient lodging options.

Where to Stay: Richfield

Tips: For the final spot at the Blackbird Mine, you may need to park and hike a short distance up the road to the mine workings. It’s a moderately steep slope to the west of the road and mine, so exercise caution.