Pioneer Day

Pioneer Day is a summer festival celebrated annually in the town of Gravity Falls, Oregon. The celebration is about the day the town was founded, including it's history and rich culture. Hosted by Pacifica's family, many of the townsfolk dress up and act as if they were in 1863 to fit in with the celebration. The festival is the main theme of the episode "Irrational Treasure."

History
Stan, while stuck in traffic, realizes that he accidentally had driven Mabel, Dipper, and himself into the fair. Stan shows a great despise for the festival, and attempts to get out of town. Dipper and Mabel appear to be interested in the festival, and decide to look around. Awhile later, the twins watch Pacifica Northwest, the supposed great-great granddaughter of the towns founder, host a speech onstage. After asking for an audience member to come up and show their Pioneer Day spirit, an intrigued Mabel goes up to introduce herself. However, she is mocked by Pacifica.

While Mabel feels the need to change her personalty, after looking through the journal, Dipper discovers that Nathaniel Northwest may not be the true founder of Gravity Falls, which would mean Pacifica's whole family is a fraud. The twins set out to figure out the government conspiracy, Mabel to prove that she isn't silly, while Dipper's reason to get back at Pacifica.

Festivities
The celebration appears to hold many festivities, such as candle-dipping and gold-panning. Old Man McGucket appeared to be "teaching" kids about the town's history in the towns library. After Stan mocks Sheriff Blubs and Deputy Durland, they toss him in "ye stocks."

Trivia

 * For an unknown reason, Stan apparently hates the celebration.
 * However, he appears to hate the Woodstock Festival as well, another annual festival that has a similar theme to Pioneer Day, possibly meaning his hatred could be general.
 * Ford, while being a visiting a researcher in the town, at some point had discovered that Nathaniel Northwest might not be the actual founder of Gravity Falls. However, he was never able to crack the code and prove this theory. During the summer of 2012, his great-niece and nephew eventually find his work and solve the mystery.