They are the first pre-Columbian stone tombs catalogued in that part of Mexico, the National Institute of Anthropology and History, or INAH, archaeologists Lourdes Garcia and Jose Beltran said.
What appear to be complete skeletons were found inside and around the 12 burial vaults, INAH said in a statement.
The experts came across the tombs amid efforts to safeguard archaeological sites in the area where crews are building a new highway to the resort town of Puerto Vallarta.
The structures lay beneath volcanic rock deposited at the time of the largest-known eruption of the nearby Ceboruco volcano, in AD 1000.
Besides the human remains, the tombs contain ceramics, tools and other artifacts that appear to date from AD 900-1100, the Late Postclassical period.
Mexico City: Mexican archaeologists have discovered a group of millennium-old basalt tombs in the Pacific coast state of Nayarit, said authorities.
First Published: Thursday, October 18, 2012, 14:46