[8] The region also sits above the eastern end of the Alvarado Ridge, an enormous uplift reaching from the Colorado Plateau to the western High Plains.

[7] Magma rising from the mantle has found a path to the surface through the Jemez Lineament, and produced a cluster of about 125 cinder cones, domes, volcanic necks, and a single shield volcano, Sierra Grande.

Prolonged volcanism has added melted lower crust to the original basaltic magma to produce andesite, such as that of Sierra Grande, and dacite, erupted as domes such as Red Mountain.

[2] Sierra Grande, the largest volcano in the field, was active during both the Raton and Clayton phases, with flows ranging in age from 3.8 to 2.6 million years.

The volcano is largely composed of two-pyroxene andesite, a rock type found almost nowhere else in the Raton-Clayton volcanic field.