Here’s a slightly edited Sunday Morning Volcano post from 2014.
Rifting in this region happened because of a complex series of events, called the Mid-Tertiary Ignimbrite Flareup, many tens of millions of years ago. During this tumultuous time volcanism was extreme throughout what are now the western United States and northern Mexico.
Things obviously have quieted down since then, but geoscientists are still keeping an eye on the southwestern US. Researchers study a magma body miles below the city of Socorro and environs, while the US Geological Survey is aware of such potential problem sites as the Zuni-Bandera volcanic field and Valles Caldera.