About a year ago, I read a story that went something like this: therapist meets with patient obsessed with visiting an old hayfield (on a slope above a river) with a strange rock formation. Therapist ends up visiting the field, and the obsession strikes him. The rocks appear to change in number and there's a mysterious dark spot within the circle. When viewed through a camera viewfinder, the number and position of the rocks will change. Therapist receives a key to the gate for the road leading to the field. Obsession overtakes the protagonist.
I cannot recall author, title or the anthology where I read it. Definitely some strong CAS and HPL flavor. Can anyone help me with information on this story?