You could map them out following a sequence of Lorenz graph plots, spanning vast periods of time. They would show up in weather patterns and earthquakes. They would show up in crime statistics, unspeakable atrocities, wars, UFO and Virgin Marry sightings. Pins on a map of natural and man-made disasters. Boulders under a fast moving stream revealed only by turbulent disturbances in the current.
Finding that pattern was next to impossible. Once found though, tracing a line forward would inevitably take the observer to a sweet spot - A precise set of coordinates where, as with finding the the stone in the stream, if you caefully trace a line back up-stream, you may find the precise place and time where you can drop a leaf and know, from any distancer, it will go neither to the left of a sand bar nor the right, but run aground like an unlucky sailor. The art is in knowing where to look, and when. The science is in narrowing the range of probabilities and tracing the line back as far as possible.
These Spots are active.