The petroglyph site at Swansea southeast of Lone Pine, California is rich in its diversity. This area was originally discovered by Professor Julian H. Steward and was recorded as his site No. 41. In addition to the numerous non-Indian inscriptions there are several groups of concentric circles that appear to serve as astronomical markers. They are located such that shafts of sunlight or shadow fall precisely in the center of a circle-group at the equinoxes or the summer solstice. No winter solstice markers have yet been found.
While time-lapse photographic observations of the sunset event by Dr. Jon Polansky during the 1985 fall equinox I noticed another set of circles nearby that looked as if it might indicate the equinox at sunrise. Although the following morning was nearly a full day after the time of the equinox I felt that it would be worth observation. The next mornings results were indeed so promising that I went to the site this spring, 1986, to observe the process on March 20.
Since the exact time of the equinox was 2:03 PM (PST) the morning event was very close to the true equinox this year. Although the set of circles was completely in shadow at sunrise, the receding shadow developed a point which passed through the center of the circles as the sun rose. This was at about 7:27:30 am or about 6 1/2 hours prior to the actual equinox.
The next morning about 17 1/2 hours after the equinox the point of the shadow missed the center by about 3/4".
This would appear to make this a very sensitive grouping which to determine the day of the equinox. Further observations can confirm its value.
About the authorMr. Yoder was companion and able assistant to Burrell Dawson on many field trips to petroglyph locations throughout the eastern California and western Nevada deserts. As a field explorer on his own he found a petroglyph site in the Alabama Hills that has demonstrated to be a specialized summer solstice observation location.
The other members of the discovery team were Burrell C. Dawson, Margaret S. Dawson and Ann Yoder. According to Vincent, It was Mrs. Yoder (Ann) who noticed the display might have been signficant when she watched the first slender dart of light approaching the center ring of the ancient work. Vincent was encouraged to write this paper on the discovery by Burrell C. Dawson, a Fellow of The Epigraphic Society.
Notes: See Analysis for a brief discussion and explanation that was the result of this important discovery.
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