Different camera - notice the fencing at around 2/3 seconds.
The monument sits at the highest point in Elbert County and is oriented to track the sun's east-west migration year-round. On an equinox or solstice, visitors who stand at the west side of the "mail slot" are positioned to see the sun rise on the horizon. An eye-level hole drilled into the center support stone allows stargazers on the south side to locate Polaris, the North Star. A 7/8-inch hole drilled through the capstone focuses a sunbeam on the center column and at noon pinpoints the day of the year.
https://www.wired.com/2009/04/ff-guidestones/