In the Grant County, western of Deming, agates do occur too. At the Bear Mountain, in the proximity of Silver City a type of Thundereggs can be found, that seems to be similar to the finds of Santa Eulalia in Mexico, the so-called Coyamo agates.

However one can constitute differences in the matrix of the Lithophysae, which is usually granular developed. Also the skin of the Lithophysae is differently to that of the Mexican Thundereggs. The agate pattern, which consists of finebanded agate formations in light-grey and pastel shades, would lie however in the range of identical agate formations from Santa Eulalia.