Geophysical Studies of The Three Sisters Andesite, West El Paso, Texas

Alexander D'Marco Garcia, University of Texas at El Paso


The Three Sisters andesite intrusion is part of series of three small igneous bodies that crop out in western El Paso to the north of the more extensive intrusions found on the University of Texas at El Paso campus and at Mount Cristo Rey. These Oligocene age intrusions are believed to form part of a deeper, more extensive igneous body that may lie beneath much of western El Paso and the southern Mesilla Valley. I used several geophysical techniques to determine the size and shape of the Three Sisters intrusion to better understand its connection to other andesite outcrops and deeper structures. Gravity was used to determine the lateral extent of the bodies below the surface and their possible connection to other intrusions. Magnetic techniques were used to further constrain the size of the intrusion and to examine variations in mineralogy of the outcrops that appear to be related to whether the andesite intruded into limestone or shale host rock. It appears the intrusions are related to narrow dikes that were the conduits from a deeper magma source and small near surface sills likely controlled by the shales.

Subject Area


Recommended Citation

Garcia, Alexander D'Marco, "Geophysical Studies of The Three Sisters Andesite, West El Paso, Texas" (2019). ETD Collection for University of Texas, El Paso. AAI27669347.