The Oscar-winning actress, who turned 50 on Saturday, made her way to Jackson Hole on Thursday where she began the festivities a couple days early at the Million Dollar Cowboy Bar.
"They said they kept it [quiet] because she sometimes likes to just act like a normal person," Southern Soul Allstars member Dianne McManus told People magazine. "They came out and danced and took a bunch of pictures."
Bullock's good friend Chelsea Handler posted one of said pictures on Instagram under the caption: "Happiest birthday." In the image, the Gravity star appears forehead-to-forehead with her sister, Gesine.
The actress continued the celebration throughout the weekend, as Chandler also shared a (NSFW) snapshot of the event Saturday with the title: "Birthday girls."