The park is where people are allowed to dig and collect the thundereggs. The thundereggs found there have typically tan to light brown rhyolite shells with wide variety of cavity shapes.  When the thundereggs were first found/dug, the agates were colorful (red, yellow, orange, pink, lavendar and light blue, but now the recently found/dug thundereggs are coming with duller colors and white to gray colors, occasionally with shadowing effects. Apparently, the thundereggs with colorful agate cores may be obtained thru old collection or lapidary stocks.