Though the seemingly ageless actress didn't hit the milestone until Saturday, Bullock started the festivities early with an evening out at the Million Dollar Cowboy Bar in Jackson Hole on Thursday.
"They said they kept it [quiet] because she sometimes likes to just act like a normal person," Southern Soul Allstars member Dianne McManus tells PEOPLE of performing for Bullock and her friends at the venue. "They came out and danced and took a bunch of pictures."
And it appears some of those photos have ended up on Instagram.
Bullock's pal Chelsea Handler posted a photo of the Gravity actress nose-to-nose with her sister, Gesine, earlier on Thursday, and comedian Whitney Cummings posted a photo of the bar's neon sign on Friday.
And the party apparently kept on going through the star's actual birthday.
"Birthday girls," Handler posted along with a cheeky (and NSFW) photo of Bullock and her friends on Saturday.