 The La <unk> region was the source of the basalt used for carving all of the colossal heads in the Olmec heartland . The La <unk> colossal head was discovered in 1970 and was the fifteenth to be recorded . It was discovered in a mountain pass in the Sierra de los <unk> , on the north side of El Vigia volcano near to Santiago Tuxtla . The head was largely buried when found ; excavations uncovered a Late Classic ( 600 – 900 AD ) offering associated with the head consisting of a ceramic vessel and a 12 @-@ centimetre ( 4 @.@ 7 in ) long obsidian knife placed pointing northwards towards the head . The offering is believed to have been deposited long after the head was sculpted . The La <unk> head has been moved from its original location to the main plaza at Santiago . 
