Anomalous Phenomena is a book that Ford Pines reads during his college days at Backupsmore University.
After completing his Ph.D. and earning a grant for his scientific research, Ford ponders what to study. He thinks about how he was teased for his six fingers, and picks up the book, Anomalous Phenomena, to peruse anomalies. This prompts him to pinpoint the town of Gravity Falls as the place with the highest concentration of these anomalies, and he decides to move there to do his research.
The book itself has information on many "odd, unusual, statistically improbable" things, including two-headed ducks and cats, crop circles, and multiple-limbed cows.