The La Venta heads are thought to have been carved by 700 BCE, but possibly as early as 850 BCE, while the San Lorenzo heads are credited to an earlier period. The colossal heads can measure up to in height and weigh several tons. The sheer size of the stones causes a great deal of speculation on how the Olmec were able to move them. The major basalt quarry for the colossal heads at La Venta was found at Cerro Cintepec in the Tuxtla Mountains, over 80 km away.