Lavas from San Martin vary between basanite and alkali basalt.

[1] Locally the volcano is also known as Tiltépetl (Black Mountain in the Nahuatl language).

San Martin forms a broad shield volcano, it rises to a height of 1680 m and is capped by a 1 km wide summit crater which is 150 m in depth.

The flanks of the volcano are dotted with 250 pyroclastic cones and maars, some of which have been active in historical times.

[3] 1793 eruption: A large VEI 4 eruption came from two pyroclastic cones in the summit, it produced widespread ashfall and lava flows that ran down the northeast flank.