BLOOMFIELD — Stew Sayah of Nederland, Colo., was visiting friends on Friday when one of them suggested they stop by Salmon Ruins on Saturday morning for the annual summer solstice celebration.
"I hadn't heard about this until last night," he said on Saturday after the event at the ruins, which are ancestral Puebloan structures located near Bloomfield that were constructed between 1088 and 1090 A.D.
The Salmon Ruins solstice event was one of four events in the area marking the longest day of the year and the official start of summer. The Farmington Public Library, Aztec Ruins National Monument and Chaco Culture National Historical Park also hosted events.
About 10 people attended the Salmon Ruins solstice ceremony, which included a tour and a chance to witness the sun shine onto a stone on an altar inside one of the rooms. San Juan County Museum Association member Brooks Marshall guided the tour.
At 7:45 a.m., sunlight shone through a reconstructed window — which Marshall created — and onto a white stone sitting on the altar inside a room.
Marshall said the altar is a unique feature at Salmon Ruins and was used to mark not only the summer solstice, but also a rare lunar event.
For three days before and after the summer solstice, this rock is lit up by the sun.
Salmon Ruins is about 30 percent excavated, Marshall said. He said if it were fully excavated, it would look like Aztec Ruins National Monument's west ruin, which is between 80 and 90 percent excavated.
"Practically, you can lay one on top of another," he said.
However, while the ancestral Puebloans spent about 35 years building the ruins in Aztec, initial construction on the Salmon Ruins took only three years. Second and third stories were added later.
The initial construction of Salmon included two round rooms — the Great Kiva, which mostly washed away during floods in 1912 — and the Tower Kiva.
The altar is located in a room just east of the Tower Kiva.
When the room was excavated, archaeologists discovered an unusual window to the room. This window had a sloped sill and an arched top.
"An arched top is extremely rare, if not nonexistent," Marshall said.
This window's purpose was to let the light in on the summer solstice, allowing it to shine onto the altar, and to let moonlight in once ever 18.6 years during what is known as a major lunar standstill. Standstills happen when the moon moves outside of the sun's "envelope," Marshall said.
Before the sun shone on the altar Saturday morning, Marshall used CDs to demonstrate this concept to the crowd.
He placed one CD at a point along a chain barrier, marking where the sun rises on the winter solstice. Then he moved to the north and placed another CD to mark the place where the sun rises during summer solstice. The distance between the two CDs represents the sun's envelope, he said.
He explained the moon usually pendulates between those two positions, except for during the standstill.
A major lunar standstill occurred in 1090 A.D., when the ancestral Puebloan people were building the Salmon site.
Another one occurred in June 2006. The next major lunar standstill is expected to occur in 2025.
During the summer solstice, the sunlight illuminates a white rock on the north side of the altar. The moon illuminates the black rock next to the white rock when it shines in during the major lunar standstills.
At that same time, the moon rises between the pinnacles of the Great House at Chimney Rock in Colorado.
"There's a nice feeling of intentionality," Marshall said.
A small wall was built in the altar room that directed light, preventing the sunlight from hitting the floor during the solstice.
"It's almost like the sunlight focuses or the moonlight focuses on that rock," Marshall said.