In a dramatic moment at UCLA's Pauley Pavilion, California First Lady Maria Shriver just strode out onto a stage that had already seen its share of celebrities -- Oprah Winfrey and Stevie Wonder among them -- and announced that she was joining the Kennedy half of the family backing Barack Obama, reports our colleague Mark Z. Barabak, who is there.

More details will be posted shortly and in tomorrow's print edition, but Shriver reportedly was waiting backstage wavering over whether she should make her support public, and then finally strode out on stage. Her husband, Republican Gov. Arnold Schwarzenegger, earlier this week announced his endorsement for Sen. John McCain.

The Kennedy family has split over the two top Democratic contenders, with Ted Kennedy joined by Caroline Kennedy Schlossberg -- daughter of his brother John F. Kennedy -- and his son, U.S. Rep. Patrick Kennedy, all going with Obama. Ethel Kennedy, widow of Robert F. Kennedy, also went with the Illinois senator.

But Hillary Rodham Clinton picked up the support of three of Robert and Ethel's children -- Kathleen Kennedy Townsend, Kerry Kennedy and Robert F. Kennedy Jr.

UPDATE: Shriver told the crowded gym that she had not intended to be at the rally, and had come straight over after going horse riding with her daughter. She joked about her appearance -- riding clothes, sans makeup and without having her hair done -- as she added her pitch for Obama.

"If Barack Obama was a state he'd be California," Shriver said, drawing roars from the crowd. "I mean think about it: diverse, open, smart, independent, oppose tradition, innovative, inspiring, dreamer, leader."

And she touched on the (see more of the blog post below the jump)...

For those of you who missed the C-SPAN coverage, it's here: