Unlike later Maya or Aztec cities, La Venta was built from earth and clay—there was little locally abundant stone for the construction. Large basalt stones were brought in from the Tuxtla Mountains, but these were used nearly exclusively for monuments including the colossal heads, the "altars" (actually thrones), and various stelae. For example, the basalt columns that surround Complex A were quarried from Punta Roca Partida, on the Gulf coast north of the San Andres Tuxtla volcano. "Little more than half of the ancient city survived modern disturbances enough to map accurately." Today, the entire southern end of the site is covered by a petroleum refinery and has been largely demolished, making excavations difficult or impossible. Many of the site's monuments are now on display in the archaeological museum and park in the city of Villahermosa, Tabasco.