Cerro Castellan on the left and Mule Ears in the distance. Info on Cerro can be found on the next page.
The "ears" are mapped as rocks of the Wasp Spring member of the Burro Mesa Formation, dated to about 29 million years ago.
These rocks record a violent volcanic eruption. The two ears are remnants of a pair of dikes, which were originally sheets of magma
forcing themselves upward through fractures in the rock. As such, they were likely feeding fissure eruptions like you may have seen around the Kilauea
volcano in Hawaii, except these were probably far more explosive. For some unknown reason, all that is left of these frozen sheets of magma are the two pillars,
triangular in profile, that side by side appear as the ears of a gigantic, crouching mule.