Earth Notes: Solstice Marker, Petrified Forest

Jun 20, 2018

Cultures all over the world have marked the passage of the seasons in many ways. In the Southwest, the solstices and equinoxes have often been tracked by watching the sun on the horizon, on particular landmarks, or on the faces of rock.

Solstice sequence
Credit NPS

At Petrified Forest National Park, one petroglyph on a boulder is a convincing calendar of the summer solstice. At Puerco Pueblo, midway between the park’s north and south entrance, there’s a small, lightish spiral pecked onto a polished sandstone slab.

For about two weeks around June 21, a beam of sunlight slants across the face of the stone, strikes the spiral, and pierces dead center around 9 a.m.

The glyph was probably created by someone living in the area in the mid 1200s to the late 1300s. It would have meant close observation of the shaft of light for some time. Then, the spiral was chipped into the precise place to form the interaction on and around the longest day of the year.  

Residents of Puerco Pueblo were farmers, and like farmers everywhere they paid close attention to the changing seasons. For them, it would have been a critical time in the agricultural cycle, as they waited for the blessing of the monsoon rains.

Today, visitors to Petrified Forest can still engage in this age-old celebration of the sun reaching its highest point in the sky. An exhibit and a short path from the pueblo lead to the marker—a place to observe and experience what sunwatchers saw a thousand years ago.