A Thunderegg has been likened to a nodule rock, which is also similar to a geode. These nodule like rocks have a rough spherical shape. They are usually the size of an orange or baseball, although there are also possibilities that they can be found in different sizes of less than an inch up to a meter across.
Thundereggs often contain centers of chalcedony material with voids and crystallization. These are the highest prizes specimens which are loved by rockhounds and collectors.
Thundereggs may appear like ordinary rocks to the untrained eye. From their outward appearance, the only indicator that they are anything more than an average rock is a spherical shape. But when one takes the liberty of slicing any piece in half as well as having it polished, that is when the most attractive patterns as well the internal contents are revealed.
Formation & Variations of Thundereggs
The formation of thundereggs is traced back to the flows of lava known as rhyolite. The gas pockets of lava act as molds where the thundereggs are formed, and silicas form within void and pockets within the lava flow.
Thereafter, the cavity of the porous rock gets filled with a dark matrix material followed by the inner agate or chalcedony core. The outside part of the thundereggs may consist of complex magmatic processes, of which the inner part may be formed and changed by getting subjected to a number of cycles of late-stage hydrothermal fluids.
Other complex processes that contribute to the formation of thundereggs include constant changes of physical as well as chemical conditions. This includes pressure, depth of formation, temperature, magma composition, ground water composition and the composition of the host rocks.
All of these variations result in the differences in each thunderegg. There are no two that look exactly alike. In fact, some of them have no chalcedony core at all, and they are actually quite boring and uninteresting to collectors. Others are simply spectacular and are highly prized.
The thundereggs can be found in a number of places. Digging is usually required, but not necessarily. I have found a lot of select pieces by simply “poking around” in the vicinity of old dig pits and searching around discarded tailing piles.
Oregon’s Public Land Thunderegg Locations
Succor Creek has long been known as a top rockhounding site in Oregon. It is a fairly remote area near the border with Idaho. The collecting area here is big. There is a lot of desert out here and many areas where good ‘eggs can hide. This area has been hunted hard over the years, yet people still come back and find more. In addition to thundereggs, there are good picture jaspers and petrified wood here that you should keep an eye out for.
Take the beautiful drive through Leslie Gulch to reach the upper end of the Owyhee Reservoir. This site is basically like Succor Creek; there is so much ground to cover and an abundance of good material. There are thundereggs as well as petrified wood, agates, jaspers, and some fossil specimens. When the reservoir levels are low in the late summer it exposes even more gravels. A rockhounder’s paradise!
This popular access is located between Prineville and Mitchell off of Highway 26. There are some nice picnic areas and campgrounds, and good agate beds that you can dig. There are dig pits all over this area and there is decent signage to help you find where to look. Find one of the old pits and start digging to recover ‘eggs. You can also walk around and explore tailings of the old pits and find some decent material to bring home and cut. White Rock Campground is just up the road and there are additional pits there as well.
*Be aware that the Mill Creek Wilderness is nearby, and no collecting is allowed within the Wilderness boundary!
Right along the northern boundary of the Mill Creek Wilderness is the Whistler Springs Campground. There are abundant collecting sites here. This is a good distance from the main road, which makes for a decent camping experience if that’s what you are looking for. The thundereggs here run smaller than what you will find at the pay-to-dig sites near Prineville, but they have nice agate material and are good prizes.
If you really want to get away from the crowds, take a trip out to the Alvord Desert in Southern Oregon and look for nice thundereggs at Pike Creek. This is one of the few year-round creeks out here, just north of the Alvord Hot Springs along the Fields/Denio Highway. You can search the creek bed, or explore the vast desert and other dry washes around this area. There is good material all over. In addition to decent thundereggs hunting, you can also find decent agate and jasper material too.
Head down to the Lakeview area for an experience away from the crowds. This site is south of Lakeview and just north of the California border. The digging pits are just a stone’s throw north of Thunderegg Lake. You can also search the gravels of Crane Creek and likely find some good material as well. This is a high elevation site and very remote, so best to save this one for summer. Go prepared and equipped for a decent hike.
Pay-to-Dig Thunderegg Sites in Oregon
This operation has been a rockhounders paradise for over 40 years now. It is famous for producing some of the finest ‘eggs in all of Oregon. This is a working cattle ranch that also operates a rock shop and several active dig sites where visitors can pay a very modest fee to dig thundereggs. Prices are based on the amount of material that you dig up and keep. They also offer an additional cutting service to cut your ‘eggs for you if you need.
There are several different diggings sites on the property. Each location is called a “bed,” and provide a different opportunity. Some are easier digging, others are difficult digging. Each bed produces a slightly different type of thunderegg. Depending on what you’re looking for, you can talk to the owners and get recommendations on where to dig.
The Lucky Strike Mine is located near Mitchell and is open to the public during the summer rockhounding season. The fees are very reasonable and the thundereggs are some of the most beautiful you will ever see!
The variety of different colors within these thundereggs is what keeps people coming back. Select pieces are absolutely stunning with agate cores containing mosses, plumes, banding, and other rare formation.
Please note that finding the mine can be difficult and will require a capable vehicle! Make sure you have proper directions BEFORE you leave home. People that rely on their smartphones to navigate in the remote parts of central and eastern Oregon should probably just stay home.
Metaphysical Properties of Thundereggs
Most people (like myself) simply enjoy collecting thundereggs for their natural beauty and as a fun thing to add to their rock collection. Of course there are also a lot of folks out there who enjoy the metaphysical properties of stones.
Many believe that thundereggs help to maintain a balance of both physical and emotional state of the body. They are also believed to have a unique energy that one can use to relieve themselves of anxiety and stress.
The thundereggs are also said to inspire honesty and integrity both in actions and words. Furthermore, the rocks can be used to treat ailments such as tumor and nodular issues. These rocks are also believed to have the ability to balance the digestive and elimination systems.
Personally, I just like to collect rocks… but if you enjoy the metaphysical properties of minerals then you will certainly be happy to add some nice ‘eggs to your collection.
Different Locations Each Produce Distinct Characteristics
One of the fun things about collecting thundereggs is that you won’t know what the inside is going to look like until you cut them open. Until you’ve cut and polished them, their internal beauty remains a mystery!
Different locations produce distinctive types of thundereggs. An experienced Oregon rockhound can usually identify where an ‘egg comes from with a quick glance. The characteristics of each dig site will produce a distinct type of internal composition.
And these variations aren’t just from each distinct location, but even as localized as the pit that you are digging in. Many areas will producing a wide array of different colored thundereggs from even a small area. Various pits will produce distinct colors and internal compositions.