Bellow you can find directions to some thunderegg collecting sites that I visited so far.
Richardson's Recreation Ranch Fee site Location: 12 miles NE of Madras on Highway 97. Directions: from Madras follow US-97 for 11 miles, turn right at NE Old US-97 (You will see Richardson's Ranch sign on right). In 2 miles turn right at NE Hay Creek Road. Follow Hay Creek Road for approx. 1 mile and Richardson's Ranch will be on your left. Web address: http://richardsonrockranch.com Contact address: 6683 NE Hay Creek Rd., Madras, OR 97741 Contact phone: (800) 433-2680 Lucky Strike Mine Fee site Location: approx. 40 miles from Prineville toward to Mitchell. Web address: http://www.luckystrikemine.com Contact address: P.O. Box 128, Mitchell, OR 97750 Contact phone: (541) 462-3073