It's peaceful, serine even. The town has been slowly healing since Weirdmaggedon and Bill, rebuilding and repairing the crumbled buildings and streets. It's all in the past now, a fading memory as time marches onward.
The Mystery Shack still stands tall, the signs posted out front ever-changing with the new themes and attractions that Soos comes up with. Dipper and Mabel have moved into town, starting up their own investigation business to look into the mysteries of this town. It's finally summer again and Stan and Ford have just gotten back from their trip to the Arctic Circle, still unpacking as they settle into the Mystery Shack once more. It's perfect, a happy ending for the loveable Pines family, but perfection can never last.
A bus pulls up to the bus stop on the edge of town, the billboard for the town is old and slightly faded as the breaks screech to a halt, the doors opening after a moment and the bus driver speaks up. "Last stop, Gravity Falls. You getting off, kid?"