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Home > Explore > Oregon Focus > State Symbols: Rock

Oregon Focus: State Symbols: Rock

A cut and polished thunder-egg.

A cut and polished thunder-egg.

On to state seal


About the Thunder-egg
Rockhounds throughout Oregon voted that the thunder-egg be named the state rock. In 1965 the legislature responded by designating it the official rock of Oregon.


Thunder-eggs range in size from less than one inch to four feet in diameter. The outside of the nodule was formed by expanding gases and is usually a nondescript brown or gray. The core is chiefly chalcedony, quartz, or opal. Sometimes it is only partially filled. They are found in areas of ancient volcanic flows and ash deposits, primarily in Wasco, Jefferson, Wheeler, and Crook counties.


Legends of the Warm Springs Indians say that these nodules were hurled from Mt. Hood and Mt. Jefferson by the "thunder spirits" who lived in the craters of the mountains. The legends say the "spirits of the mountains" robbed the nests of the thunderbirds and hurled the "thunder-eggs" to the accompaniment of much thunder and lightning.


Thunder-eggs make fine jewelry, bookends, paper weights, and other decorative objects when cut and polished.


Thunder-egg jewelry. Photo courtesy

Thunder-egg jewelry. Photo courtesy

Suggestions for teachers
Ask students to:


Bring in thunder-eggs and set up a place to display them.


Share information about their rocks through show-and-tell or question-and-answer periods.


See an uncut thunder-egg and jewelry made from them.


Locate on maps where thunder-eggs are found.


Visit a rock show or museum. Watch a demonstration of how rocks are cut and polished.


Invite a "rock hound" to show-and-tell.


Go "rock hounding."


Discuss how rocks are formed.


Study volcanoes or rock formations to discover the source of thunder-eggs.


Discuss the related Native American legends.


On to state seal