Greene Robertson; thereafter every few years leading Mayanists would meet at Palenque to discuss and examine new findings in the field. Meanwhile, Robertson was conducting a detailed examination of all art at Palenque, including recording all the traces of color on the sculptures. The 1970s also saw a small museum built at the site. In the last 15 or 20 years, a great deal more of the site has been excavated, but currently, archaeologists estimate that only 5% of the total city has been uncovered. In 2010, Pennsylvania State University researchers, Christopher Duffy and Kirk French, identified the Piedras Bolas Aqueduct as a pressurised aqueduct, the earliest known in the New World. It is a spring-fed conduit located on steep terrain that has a restricted outlet that would cause the water to exit forcefully, under pressure, to a height of . They were unable to identify the use for this man-made feature. In June 2022, archaeologists from the Mexico's National Institute of Anthropology and History (INAH) announced the discovery of a 1,300-year-old nine-inch-tall plaster head statue indicating a young Hun Hunahpu, the Maya’s mythological maize god. The figure's semi-shaved haircut that resembles ripe corn gives reason to the possibility that it is a young maize god. Researchers assume that the Mayan inhabitants of Palenque possibly placed a large stone statuette over a pond to represent the entrance to the underworld. According to archaeologist Arnoldo González Cruz, the Mayan people symbolically shuttered the pool by breaking up some of the plaster and filling it with animal remains, including pottery fragments, carved bone remains, shells, obsidian arrowheads, beads, vegetables, and others. Palenque National ParkPalenque National Park''' was designated in 1981 by the Mexican government. It covers an area of 17.72 km2, which encompasses the ancient city and the hills to the south. The park includes a family camp site. See also List of Mesoamerican pyramids List of megalithic sites Maya script Temple 20 Notes References (1963). The Palenque Triad. Journal de la Société des Américanistes, n.s. 5(52):91–99. Paris. (2005). The Mask Flange Iconographic Complex [electronic resource]: The Art, Ritual, and History of a Maya Sacred Image. Doctoral dissertation, The University of Texas at Austin. Available electronically from http://hdl.handle.net/2152/1027. and (2002). The Cosmogonic Symbolism of the Corbeled Vault in Maya Architecture. Mexicon Volume XXIV, No. 2, April. (1991). Iconographic heritage of the Maya Jester God. In Sixth Palenque Round Table, 1986. Virginia M.