Opal Butte lies in the Morrow County in Oregon. The place of discovery was claimed until 1988 by Dale Huett (Westcoast Mining). Beside beautiful noble opals in the varieties of contraluz-opale, rainbow-opale and fire-opale the core of the thundereggs was formed by agate layers and common opalite. The Thundereggs  were reaching sizes up to 40 cm..