SAN FRANCISCO — America Ferrera was exhausted. Two weeks on the road to promote "The Sisterhood of the Traveling Pants" — a different city every day, never enough sleep, eating at odd times — took its toll on her ailing co-star Alexis Bledel, who missed out on this final day of the tour.

That film opened in theaters across the country on Wednesday, and she's also in a film that opened today, "Lords of Dogtown" (as a character named "Thunder Monkey").

"I am sooooo tired," the 21-year-old Ferrera said, stabbing at a green salad, her "pre-lunch," she called it. So pardon her if she talks with a full mouth. She has things to say and places to go.

Ferrera, giggly and animated, would tell her story one more time and then catch a flight to New York where she would choose an outfit for the film's Los Angeles premiere. She'd finally catch up with Bledel and their castmates Amber Tamblyn and Blake Lively on the red carpet.

"We got very lucky that they put us four girls together, because we had a lot of chemistry, and we really like each other in real life, so that made it easier to play it on screen," Ferrera said. "When we are all four together, it's like a distinct personality. We're not really whole until we're all together."

In "The Sisterhood of the Traveling Pants," based on the best-selling novel by Ann Brashares, they play lifelong best friends who, during the summer of their 16th year, will be apart for the first time.

Ferrera, who got rave reviews for her leading performance in "Real Women Have Curves" (2002), plays the fiery but sensitive Carmen, who is excited about spending time with her dad (Bradley Whitford of "The West Wing"), whom she has not seen much since he divorced her mom years ago.

Together at a vintage-clothing store before they separate, the girls buy a pair of jeans that magically fits each of their very different body shapes. They decide to share the pants over the summer, as a way of staying in touch and to bring them all good luck.

The time apart will prove an unforgettable rite of passage for each girl.

"We all know how special this project is and how lucky we are to be a part of it," Ferrera said. "I just love that it's so real and so honest. It's this portrayal of being young that we don't see so often in movies, which is that young people are just as complex and just as layered and just as strong as any other grown-up."

Ferrera's character is the story's narrator.

"We'd been a foursome for as long as I could remember," Carmen says early on. "We depended on each other to understand things that no one else could, and to be there for the things we couldn't face alone."

"I love Carmen," Ferrera gushed. "She's flawed, and there are moments when she does selfish things, but you don't blame her. She doesn't ever become a villain, because she's so human."

Ferrera said the film appealed to her because it showed the value in friendships. "Teenage girls are sometimes portrayed so negatively these days," Ferrera said. "Girls are competitive and backstabbing and conniving, and we're always each other's enemy. This movie shows how beautiful and fulfilling and valuable those relationships can be, because we're all going through the same things in our lives, and it would be silly not to look to each other for support."