Ruins’ holes mark solstice By BRIAN AHNMARK, Casa Grande Valley Newspapers Inc.
The Hohokam could easily be considered prehistoric astronomers.
Researchers and visitors alike have long questioned the significance of mysterious holes bored through the walls of the Big House at the Casa Grande Ruins National Monument.
The holes – five in the east wall, one in the south, one north, and two west – appear to serve as a primitive seasonal calendar, indicating the spring and autumn equinoxes as well as summer solstice and lunar events. However, researchers can merely speculate what purpose this celestial understanding served for the Hohokam culture, which flourished about 700 years ago.
CGRNM Ranger Denise Shultz defines four major astronomical holes: a summer solstice alignment hole in the north end of the west wall, a lunar alignment hole in the south end of the west wall, and towering four stories high in the center room of the Casa Grande are the spring and fall equinox holes – one in the east wall, one in the west.
“The summer and lunar events are a little more difficult to see happen because there aren’t any floors anymore, so you’re not at the right viewing level,” Shultz said. “But the equinox alignment is still visible.”
Just after sunrise, a beam projected through the east wall hole onto the west wall slowly approaches and then aligns perfectly with the west hole. This happens around the spring and fall equinoxes each year. Shultz said that the timing isn’t always exact, but the alignment does only occur two days a year. …
In 1969, the Southwestern Archaeological Center contracted John Molloy, an anthropology graduate student at the University of Arizona, to investigate the supposed seasonal holes.
Along with D.H Kayser, an assistant ranger at the Ruins, Molloy identified 14 lunar and solar holes. They discovered that two east wall holes align with the sun during the spring and fall equinoxes approximately 15 minutes after sunrise, on March 7 and October 7 of every year. They also observed the setting sun of the summer solstice, the longest day of the year, align with a hole in the west wall of the Casa Grande. This event continues to occur around June 21.
Molloy argued that the celestial implications of the holes showed Mesoamerican influence, but did not suggest a meaning or use for the solar and lunar data that the Hohokam may have observed. The Hohokam culture disappeared around 1450 A.D., leaving no explanation for the mysterious holes in the Casa Grande.