PIC: Nicole Richie Strips Down to Bikini for Post B-day Weekend

Credit: Clasos.com/Splash News

After partying at her Beverly Hills 30th birthday bash on September 21, Nicole Richie has taken the celebration south of the border.

The married mom of two enjoyed some fun the sun with fruity cocktails and close pals including Samantha Ronson (who also sported a two-piece) in Los Cabos, Mexico Friday.

Clad in a tiny black bikini by Eres, the birthday girl flaunted her healthy figure but showed no sign of vegging out on the massive three-tier birthday cake at her A-list party two days prior, where she gathered a bevy of family and friends like her hubby Joel Madden, Ronson, Mary-Kate Olsen, Benji Madden and dad Lionel Richie at a deluxe suite at the Beverly Wilshire.

"I can't believe the outpour of birthday love I am getting on twitter today!" Richie wrote on her Twitter account September 21. "From the bottom of my heart (& the top), THANK YOU SO MUCH!"