Las Cruces is a major city. Las Cruces/El Paso/Juarez together comprise a metro area nearing 2 million people.
Dripping Springs Road/University Ave exit is off of I-25 very near the I-25/I-10 interchange south of Las Cruces (about 35 miles N of the main part of El Paso).
Regarding the geology, I can only speak in general terms. It's obvious a volcanic range (as opposed to sedimentary). I doubt it was once a volcano though. Likelier the result of uplifting and other ancillary acts of volcanism.