The Sun Dagger of Fajada Butte

First documented by a researcher in 1977, the effect no longer occurs as it once did: the rock slabs that created it shifted position in 1989, apparently as a result of erosion from visitor traffic to the site — an ancient astronomical marker altered within living memory by the attention it received.

Anna Sofaer's 1977 observation of the solstice light effect; the 1989 slab shift