Annette Bening explores motherhood and mood swings in her latest gem, '20th Century Women'

Annette Bening as Dorothea and Billy Crudup as William in "20th Century Woman."

'Sometimes I have an almost involuntary, intuitive reaction about a character - a light goes off in my head," said Annette Bening, confessing that she didn't have that response when she first read Mike Mills' script for 20th Century Women.

Here was Dorothea Fields, a single mother who runs a makeshift boardinghouse in Santa Barbara, who sits each morning with her teenage son to pore over her stock investments, who smokes like a chimney and has a rueful view of the world - the world as it looked in 1979. As Bening considered what to make of the character, how to play Dorothea, nothing at first "popped out."

"I loved the screenplay," the actress said, on the phone from New York recently. "I grew up in California, so, for me, this was a story about where I grew up, when I grew up. And that kind of blew my mind, quite frankly, and I just looked at it through that prism. But this woman, Dorothea, I didn't really know who she was. I found her very enigmatic."

Not to worry. Audiences may find Bening's portrayal of the bohemian mom who listens to old jazz songs and dreams of piloting a biplane - and who recruits two younger women, played by Elle Fanning and Greta Gerwig, to help guide her child through the messy terrain of adolescence - a bit of a puzzle. But it's the kind of puzzle, with pieces drawn from real life, that forms a blazing, fully realized character, full of contradictions, passion, heartache.

And just as writer and director Mills modeled the role of the father in his 2010 film, Beginners, on his own dad (Christopher Plummer played the part, and won an Oscar for his efforts), Dorothea in 20th Century Women was very much based on Mills' late mother.

"The more I talked with Mike about his mother, the more intrigued I became," Bening said. "I would hear lots and lots and lots about his mom. And I spoke to his sister, who is an astrological reader - and I am a Gemini, and their real-life mom was a Gemini - and she did this reading, which was hilarious. . . .

"But I got this take on Mike's mom from his sister which was quite different than his. So it was a fascinating process of searching, and wondering, and a lot of intellectualizing at first, but then when we got down to shooting, it was very open. I had a kind of quiet mind about what might happen and how Dorothea might react in any situation. And I wanted that. I wanted that sense of exploration and freedom."

Bening is 58 now - just about the age Dorothea is in Mills' movie. The relationship between mother and son Jamie (finely played by newcomer Lucas Jade Zumann), is a tangle of parent/child dynamics. Sometimes Dorothea doesn't know how to react to her son's behavior, his moods, his immersion in feminist texts, say. Sometimes they hit it off, brilliantly.

Here's one kernel of wisdom Dorothea imparts to Jamie: "I just think that having your heart broken is a tremendous way to learn about the world."

"I love that line," said Bening, who has raised four kids with her husband of 24 years, some guy named Warren Beatty. (They met on Barry Levinson's 1991 mobster epic, Bugsy. Sparks flew.) "And, of course, it's true. None of us want to have to say that to our children - but we have to."

For her tenacious and downright beautiful performance in 20th Century Women, Bening was nominated for a best actress Golden Globe (Emma Stone won, for La La Land, last Sunday), a Gotham Award, and an Independent Spirit Award. Be very surprised if she doesn't likewise nab a best actress nomination when the 2017 Academy Award contenders are announced Jan. 24. 20th Century Women opens Friday at the Ritz East.

Bening was a theater major at San Francisco State University during the time 20th Century Women takes place. "I moved to San Francisco in 1978, and that was the fall when Dan White killed Harvey Milk and George Moscone," she said. "Talk about a turning point in that city and that culture, my God! It just totally shifted everything. And then, of course, the next year AIDS hit. It was like a tsunami in that city."

The actress didn't make her move from theater to film for almost a decade after she left school. Her screen debut: 1988's Dan Aykroyd/John Candy/John Hughes comedy The Great Outdoors. It didn't take long, though, for audiences and critics to sit up and notice: Looking a bit like Gloria Grahame with big '80s hair, Bening gave a sly turn as a con artist in The Grifters (1990) that gained her a supporting actress Oscar nomination. Three more Academy Award nominations followed: for her role as the cold, materialistic spouse in American Beauty (1999), as the glamorous English diva who falls into an affair in Being Julia (2004), and as the lesbian obstetrician and parent in The Kids Are All Right (2010).

In November, Bening was the subject of an American Film Institute tribute. She sat onstage (interviewed by Kids Are All Right director Lisa Cholodenko) and reflected on her career. They showed clips. They showed 20th Century Women.

"One of the good things is that the further away you get from the movies you made, fewer memories pop into your head," Bening said, laughing. "When you're watching yourself in movies, you're always thinking about all the other things that were going on while you're making the movie, that have nothing to do with the movie, that nobody else would ever think about when they were watching the movie.

"But when enough time passes by, you just can't remember what was going on, so you begin to see the movie a little bit more how other people see it."

Bening says that coming up through the theater - the Colorado Shakespeare Festival, the American Conservatory Theatre, a Tony nomination for Coastal Disturbances at Circle in the Square Theatre - it wasn't possible to see her performances, to scrutinize her work after the fact. You do a play, you call it a night. You do a film, it's all there in front of you, up on the screen.

"I had never had to see how I looked when I felt a certain thing, or was doing a certain thing, and at first it was quite jarring," she said. "But it's very important for me, because there's so much to be learned from watching yourself. Even technical things, about the camera, there's so much to be learned. . . .

"And there are times when I'm really proud of myself, I think, 'Oh, that was good.' But, generally speaking, there is not a film that I've done where, if I had some magic wand and I could pop myself back into that film and say, 'Let's do it again,' I wouldn't want to go back and do it over, make it better."

steven.rea@yahoo.com

@Steven_Rea