Thunderegg Days

On the Nyssa Elementary School lawn at 809 Bower Avenue, vendors set cut and polished thunder eggs on their tables to catch the eye of passersby. According to the Argus Observer, the rocks are abundant in the Owyhees and have been a constant centerpiece of the festival. Other vendors sell gemstones, art and crafts, and local food vendors sell meals. The Nyssa Chamber of Commerce runs the festival from Thursday through Saturday, 10 a.m. to 9 p.m. each day, with no admission charge. Its notice for the 2026 festival, held July 9 to 11, called it “the hottest weekend around.”

Local activities and entertainment fill the three days. The 2025 program included fundraiser breakfasts, movies, and a ribbon cutting held jointly by the city and the chamber. Many booths belong to working rock shops. Kurt and Charlene Branham of Parma, who operate Earth Bright Rock and Gem Shop in Caldwell, had one in July 2019. After the 2026 festival the chamber posted a lost-and-found notice for items left on the picnic tables near the Latin Assembly of God, which could be claimed at Nyssa City Hall. It also thanked the sponsors, volunteers, vendors, city organizations and the Nyssa School District: “Community events like this wouldn’t be able to continue without help from the community itself.”

The rock on the tables

In 1965 the Oregon Museum of Science and Industry asked Oregonians to choose a state rock. The Oregon Encyclopedia reports that voters picked the thunder egg “by a landslide,” in the Oregonian’s words. The state Department of Geology and Mineral Industries says the 1965 Legislature named it after rockhounds throughout Oregon voted it first choice. The legislature described it as a “remarkable and colorful agate-filled spherical mass of silicified claystone, and rhyolite.”

Thundereggs range from less than an inch to more than four feet across. They form in welded tuff or perlitic rock and are found chiefly in Crook, Jefferson, Malheur, Wasco and Wheeler counties. The outside is nondescript. When the rock is cut and polished, the inside shows agate, jasper or opal in a wide range of colors.

A 1969 issue of The Ore Bin, the department’s bulletin, says there appear to have been at least two stages in their making. First, small gas pockets formed explosively in a semi-solid, light-colored lava flow. Later, the pockets filled with agate or opal. The same bulletin gives an older account of the name. The thunderegg may owe it to a legend of the Indians of central Oregon, in which the rocks were missiles hurled from the craters of Mount Hood and Mount Jefferson whenever the gods living in those mountains became angry.

A steam whistle and 42 rockhounds, 1966

The Ore Bin dates the festival to 1966. That year Nyssa proclaimed itself “The Thunderegg Capital of Oregon” and held a three-day celebration that, by the bulletin’s count, brought 3,000 visitors and collectors from 42 states. The Nyssa Gate City Journal printed the slogan on its masthead. On August 11, 1966, it reported that the town had hosted more than 3,000 out-of-towners over a weekend when both Thunderegg Days and a Union Pacific steam locomotive came through.

The train carried 613 passengers, mainly model railroad enthusiasts bound for a convention in Boise. It ran about half an hour late, and Nyssa policemen spent the wait keeping children off the track. When the engine pulled into the depot on Saturday afternoon, a group of musicians played welcoming tunes, and children held their hands over their ears as the whistle blew long and loud.

Harold Brendle, chairman of Thunderegg Days, was “extremely well pleased with the event and proud of the reception given the visitors,” the Journal reported. Forty-two visiting rockhounds signed a letter to the city dated August 5, 1966. It thanked Nyssa “for the splendid hospitality extended to the rock hounds” and for “the privilege of staying in your park,” and noted that “the rocks were very well displayed.” The signers came from British Columbia and Alberta, from Los Angeles and Nevada City in California, from Illinois and Washington, from Portland, Gresham and Sweet Home in Oregon, and from Sandpoint, Caldwell, Nampa and Emmett in Idaho.

The only complaint the paper recorded was the heat. Temperatures rose above 100 degrees on Wednesday and Thursday, though some visitors said they expected heat in a semi-desert valley. The sources disagree on the co-sponsor. The Journal names the Chamber of Commerce and the Snake River Gem club. The Ore Bin names the chamber and the Treasure Valley Gem and Rock Club as annual sponsors.

A fence around South Park, and a 60th year

The calendar has moved more than once since then. The 1966 festival fell in early August. A state geology department page gives five days around the first of June. The festival now runs three days in July.

In June 2020, as Oregon reopened from the COVID-19 lockdown, chamber board member Jason Pearson asked the Nyssa City Council for use of South Park. The chamber proposed a portable fence around the park, physical distancing, and hand-washing stations or sanitizer. Its plan relied on outdoor guidelines that then allowed gatherings of up to 250 people, and City Manager Jim Maret said he would confirm that with the state. Chamber President Tawni Maxwell reported that more than 20 vendors had signed up. “People are wanting to come,” she said. “Nyssa really needs stuff to open up,” Pearson said. The council voted unanimously in support of the festival, which was set for July 9, 10 and 11.

In 2025 it was unclear for a few months whether the Nyssa Chamber of Commerce and Agriculture could put on the festival at all. A newly organized chamber did so, with involvement from city officials, and held the 60th annual Thunderegg Days on July 10 to 12. The City of Nyssa’s website now heads its pages “The Thunderegg Capital of the World.”