From a post by T. McGinnis at this website:

"White Rock Springs
What: Jasper Thundereggs
The eggs are of agatized jasper composition with rhyolite matrix, in many
color combinations: browns, tans, yellows, reds and mauves. Many unusual shades
and patterns are formed in each thunderegg. The size may be only one inch in
diameter up to several feet, depending upon the depths at which eggs are found.

Agency: Ochoco National Forest
Directions: Follow US 26 to milepost 41. Turn left on Road 3350, then right
on Road 3350-300, about 7 miles total.
Tools: Rock hammers, picks and shovels only.
Note: Materials is hard to find, but very beautiful. Carnelian cores have
been found in the area.
CAUTION: Watch for the Mill Creek Wilderness boundary signs."