Sierra de los Tuxtlas
The Sierra de Los Tuxtlas (Tuxtlas Mountains) are a volcanic belt and mountain range along the southeastern Veracruz Gulf coast in Eastern Mexico. The Los Tuxtlas Biosphere Reserve (Biósfera Los Tuxtlas) includes the coastal and higher elevations of the Sierra de Los Tuxtlas.
The volcanic mountains were used as a basalt source by the Olmec culture during the Early Formative period (1500 BCE to about 400 BCE). Quarried basalt was transported by raft through a network of rivers, to sites in the Olmec heartland for use in creating monuments, including colossal heads. 
Peaks in this range include Volcano Santa Marta and Volcano San Martín Tuxtla, both rising above 1700 meters. San Martín Tuxtla is the only recently active volcano in the belt, erupting in 1664 and again in May 1793. It is a broad alkaline shield volcano with a one kilometer wide summit. Hundreds of smaller cinder cones are prevalent throughout the Sierra.
Other, extinct volcanoes include San Martin Pajapan (1,160 meters) and Cerro El Vigia (800 meters).
The Sierra de Los Tuxtlas volcanoes are an insular anomaly. The volcanoes are separated from the nearest volcano in the Trans-Mexican Volcanic Belt to the west by about 150 miles (250 km), and from the Central American Volcanic Belt to the southeast by almost 200 miles (330 km).
The upper flanks of the San Martin Tuxtla and Santa Marta volcanoes are covered with the neotropical Sierra de los Tuxtlas tropical rainforest ecoregion, of the Tropical and subtropical moist broadleaf forests Biome. The lower portions are covered with stunted pastures and grasslands.
- Ancient Mexico and Central America
- Yarza de la Torre, Esperanza (1971). Volcanes de México. Aguilar. p. 237 pp. (in Spanish)
- "San Martín". Global Volcanism Program, Smithsonian Institution. http://www.volcano.si.edu/world/volcano.cfm?vnum=1401-11%3D.