The grayish thundereggs were found by accident near Mesquite Creek when the plowing was done to make a new road up the south side of the hill where Laguna agates are found. They came from white to clay beds (decomposed greenish perlite/tuff?) underlaying the agate-bearing basalt beds throughout the area. Several locations around the Mesquite Creek have produced similar thundereggs. The agates generally have watered-down dark red to yellow colors, and those with brighter colors do come up.