Trembley's Cove

The underground cave is a hidden location underneath the Gravity Falls Cemetery, accessible by pullimg down on the arm of an angel statue. It contains many historical artifics, specifically documents.

History
"Irrational Treasure", Dipper and Mabel Pines set out to uncover the truth as to whether or not Nathaniel Northwest is the founder of Gravity Falls, Oregon. After following a series of clues, the twins find the cave, thanks to Mabel pretending an angel statue is picking her nose. The two descend a set of stairs they unearth and, in an underground corridor, accidentally set off a trap that shoots traquilizer darts at them; they quickly run through and make it to the end of the main part of the cave unharmed. There, they find many historical docements on historical secrets, including the one they are searching for, the Northwest cover-up, as well as other artifacts. They read the document and learn the identity of the real founder of Gravity Falls: Quentin Trembley.

Soon, Sheriff Blubs and Deputy Durland arrive, finding their way by following Mabel's trail of candy wrappers, and confront the twins. However, they are delayed by Durland fainting, due to being hit with an excessive amount of darts. After Durland comes to, he and his associate show Dipper and Mabel a film regarding Trembley, showing how he won the election in a literal landslide and did such a great number of silly and "shameful" acts that he was removed from office. Then, the film shows him fleeing to an uncharted valley in Oregon which he deemed "Gravity Falls" after falling of a cliff at high speed. The documentary then ends, and Sheriff Blubs shows the twins Trembley's body encased in a block of solid peanut brittle. Blubs and Durland then ship the twins, Trembley and the artifacts to Washington, D.C.