All seventeen of the confirmed heads in the Olmec heartland were sculpted from basalt mined in the Sierra de los Tuxtlas mountains of Veracruz . Most were formed from coarse grained dark grey basalt known as Cerro Cintepec basalt after a volcano in the range . Investigators have proposed that large Cerro Cintepec basalt boulders found on the southeastern slopes of the mountains are the source of the stone for the monuments . These boulders are found in an area affected by large lahars ( volcanic mudslides ) that carried substantial blocks of stone down the mountain slopes , which suggests that the Olmecs did not need to quarry the raw material for sculpting the heads . Roughly spherical boulders were carefully selected to mimic the shape of a human head . The stone for the San Lorenzo and La Venta heads was transported a considerable distance from the source . The La Cobata head was found on El Vigia hill in the Sierra de los Tuxtlas and the stone from Tres Zapotes Colossal Head 1 and Nestepe Colossal Head 1 ( also known as Tres Zapotes Monuments A and Q ) came from the same hill .