 The colossal heads cannot be precisely dated . However , the San Lorenzo heads were buried by 900 BC , indicating that their period of manufacture and use was earlier still . The heads from Tres Zapotes had been moved from their original context before they were investigated by archaeologists and the heads from La Venta were found partially exposed on the modern ground surface . The period of production of the colossal heads is therefore unknown , as is whether it spanned a century or a millennium . Estimates of the time span during which colossal heads were produced vary from 50 to 200 years . The San Lorenzo heads are believed to be the oldest , and are the most skillfully executed . All of the stone heads have been assigned to the Preclassic period of Mesoamerican chronology , generally to the Early Preclassic ( 1500 – 1000 BC ) , although the two Tres Zapotes heads and the La Cobata Head are attributed to the Middle Preclassic ( 1000 – 400 BC ) . 
 The colossal heads cannot be precisely dated . However , the San Lorenzo heads <a href='uninflect' title='1'><mark>were</mark></a> buried by 900 BC , indicating that their period of manufacture and use was earlier still . The heads from Tres Zapotes <a href='been_done' title='2'><mark>had</mark></a> been moved from their original context before they <a href='uninflect' title='3'><mark>were</mark></a> investigated by archaeologists and the heads from La Venta <a href='uninflect' title='4'><mark>were</mark></a> found partially exposed on the modern ground surface . The period of production of the colossal heads <a href='drop_aux' title='5'><mark>is</mark></a>therefore unknown , as is whether it spanned a century or a millennium . Estimates of the time span during which colossal heads <a href='uninflect' title='6'><mark>were</mark></a> produced vary from 50 to 200 years . The San Lorenzo heads are believed to be the oldest , and are the most skillfully executed . All of the stone heads <a href='been_done' title='7'><mark>have</mark></a> been assigned to the Preclassic period of Mesoamerican chronology , generally to the Early Preclassic ( 1500 – 1000 BC ) , although the two Tres Zapotes heads and the La Cobata Head are attributed to the Middle Preclassic ( 1000 – 400 BC ) . 
Da colossal heads cannot b precisely dated . However , tdaSan Lorenzo heads was buried by 900 kus , indicating that their period of manufacture and use was earlier still . Thdaeads from Tres Zapotes done been moved from their original context b4 they was investigated by archaeologists and the heads from La Venta was found partially exposed on thedadern ground surface . The period of production of the daossal heads therefore unknown , as is whether it spanned a century or a millennium . Estimates of the time span during which colossal heads was produced vary from 50 to 200 years . The San Lorenzo heads r believed to be the odast , and are the most skillfully executed . alll of the stda heads done been assigned to the Predassic period of Mesoamerican chronology , generally to the Earldareclassic ( 1500 – 1000cusC ) , although the 2 Tda Zapotes heads and the La Cobata Head are attributed to the Middle Preclassic ( 1000 – 400 BC ) .