Trilobites and the House Range

Two Species of Trilobites at the Same Time!

My son, Evan, and I went out past Delta yesterday to go dig fossils at the U Dig Fossil quarry near Swazey Peak in the House Range.  The quarry is located where a very rich vein of the Wheeler Shale is exposed and one can find very well preserved trilobite and other fossils from the Cambrian era (half a billion years ago).  It costs $28 per adult for two hours and you get a 20% discount if you can show them a Utah driver's license.  They give you a rock hammer and a bucket and you are allowed to cart off as much rock as you want during your stay.  The quarry is dug out periodically with power equipment so there are fairly fresh shards of shale to work with.  You try to split the rock along a seam layer and hopefully expose a fossil when you do so.  Most of the fossils are trilobites and are very small and often just pieces.  Sometimes you find only an impression because the fossil itself is fragile and breaks up when you split the rock.  The biggest ones we got were an inch or two long.

Dugway Geode Beds

I've made this trip three times, always with the boy scouts. First in the Fall of 1999, and then again in the Spring of 2005 and Spring 2008. This is a fun trip out into the middle of an arid wasteland with its own stark beauty. The trip is 2-3 hours from the Wasatch Front, depending on where you live and how fast you are willing to drive over the dirt roads. You could do it as a day trip, but I've always done it as an overnighter. The last two times we backpacked in from the road. The reward at the end is digging for small geodes; spheres of crystal that are often hollow. They look round and fairly dull on the outside, but are quite beautiful on the inside. (Like me!)

Here are the directions to get there from Orem:
1. Head north on I-15 N toward Salt Lake
2. Take exit 279 for Main St toward Lehi 0.3 mi
3. Turn left at E Main St 1.3 mi
4. At the traffic circle, take the 2nd exit onto W Main St 3.1 mi
5. Continue on W 8570 N/UT-73 25.5 mi
6. Turn right at Faust Rd 13.6 mi
7. Head south on UT-36 0.1 mi
8. Turn right toward Hatch Ranch Rd 12.6 mi
9. Turn left at Hatch Ranch Rd 0.1 mi
10. Turn right at Lookout Pass Rd 1.2 mi
11. Slight right toward Simpson Springs Rd 11.9 mi
12. Turn left at Simpson Springs Rd 0.8 mi
13. Turn right at Pony Express Rd 3.4 mi
14. Head southwest on Pony Express Rd/Simpson Springs Callao Rd 23.3 mi

Once you get to the turnoff from the Pony Express Road you need to either park and walk in couple of miles, or drive. The vast majority of people drive. It's no problem with a 4WD and you can do it with a 2WD if you are careful at a few bumpy spots. There are roads of various quality all over here and finding the digs can be a bit of a challenge. Below are a couple of maps that may help. The topographic maps of the area are way out of date when it comes to the roads and 4WD trails, so ignore them. But the lay of the land hasn't changed, so they are helpful in that regard.

Topographic Map of the Area

Sketch of the roads, not to scale, but accurate as of Spring 2008

The mineral rights here are privately owned, even though this is public land. You are apparently free to glean through the pits the owners have dug to hunt for big geodes. A shovel and a bucket are a big help, but not strictly necessary. A hammer would help too, if you need an immediate payoff for the long drive, but you should try to save your more promising finds for when you get back to town. You can saw them open with a rock or tile saw, and they are much more attractive that way.

Geodes form when water seeping through the rock deposits minerals into cavities. Over the eons the minerals build up in layers, that can often be seen in cross section when you cut open the geodes. The surface layer is usually crystals and is very pretty. At the Dugway site, the rock is mostly volcanic; primarily Rhyolite. It's a fairly soft whitish rock, and the crystals that form in the cavities are much harder than the surrounding rock. When the rock is exposed by weathering, it erodes away relatively quickly leaving the harder lumps of minerals behind. These roll down the mountainsides and are washed down further when there is heavy rain. Virtually all the good sites at Dugway are near dry washes and are in loose dirt deposited by seasonal rainstorms.

View of the main digs, Spring 2008

Geode sample from Spring 2005

Here's the location in Google Maps. The map and terrain views show the current 4WD roads fairly accurately if you zoom in.

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Iron Concretion Spheres at Rochester Creek

Last May I visited the Rochester Creek Pictograph Panel just east of Emery, on the edge of the San Rafael Swell. The panel is impressive and I'll try to write up something about it at a later date. While we were there we noticed some odd stains on the rocks near the panel. At first I thought they were bird droppings, but it turns out they were iron concretions in the sandstone.

We mistook these stains for bird droppings

The Fremont sandstone here is very pale and not nearly as red as some other places in Utah. This is due in part to the iron (in the form of hematite) leaching out of the sandstone over the eons as water percolates through it. The iron eventually accretes into small marbles of iron. These are often called "Moki Marbles" or "Moqui Balls." They are frequently found in the lower layers of the Navajo sandstone. In some places on the Colorado Plateau the marbles are almost pure, solid iron. Here they look to be mostly iron oxide and they have formed into shells, with interiors of sandstone. As they weather away they are exposed on the surface of the rock as rings and the weathering stains the rock around them.

A pdf file from the State of Utah, Rainbow of Rocks, explains all this.

A closeup of the exposed and weathered concretions

A closeup of an exposed sphere

A dense concentration along the path to the rock art panel

Here is the location of the rock art panel and these concretions in Google Maps:

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Concretion Spheres in Short Canyon

This past October I drove down to the San Rafael Swell with my two sons and we did a couple hours of exploring/hiking along and near the Moore cutoff road. We stopped at the pictograph boulders near the road just after the road descends through Molen Reef. A few miles beyond this there is a less developed road heading north which takes you to Short Canyon. Here we saw some very interesting geology.

There is a layer of the Mancos shale here where you will find huge spherical boulders. These are concretion spheres that apparently formed by chemical accretion in a warm shallow sea. Many of these boulders are 15 feet or more in diameter. They can be seen very clearly along the north wall of the canyon, but they can also be seen in the south wall if you look closely. As you drive or walk further up the canyon the elevation of the canyon floor rises and the boulders eventually get close enough that you can easily climb up and examime them.

This is a geological oddity that is well worth a side trip if you are in the area.

Wikipedia explains how these form.

Here is a shot of the layer of shale with the boulders

A telephoto view of some of the boulders; these are 10 - 15 feet in diameter

A close-up of a sphere further up the canyon

Another sphere that has extensive weathering - notice how it erodes in layers like an onion

Alan strikes a heroic pose. This photo is mostly to give a sense of scale.

Here is the location of Short Canyon in Google Maps.

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