Already, though, she's contemplating another book project.
"I'd love to do a book on Cliff May," Keaton said, referring to the San Diego architect who pioneered ranch-style homes in the 1930s.
Keaton drives south from Hollywood several times a year to attend board meetings at the Helen Woodward Animal Center in the upscale San Diego County community of Rancho Santa Fe, where she also serves as a spokeswoman for its Iams Home for the Holiday pet adoption drive.
Preservation is not just another role for Keaton, whose almost 40-year career includes movie classics such as "Annie Hall," "Reds" and "Something's Gotta Give." Honors include a 2004 Hero Award from the National Trust and the Walden Project for spearheading a successful restoration of a Frank Lloyd Wright masterpiece, the Ennis House, and failed efforts to stop demolition of the Ambassador Hotel, both in Los Angles.
"She is very active and very committed. She's been willing to use her celebrity to bring people to the table," said conservancy director Linda Dishman. "She has a very engaging personality, and it's been a real joy to watch her with people who aren't into preservation and see her bring them in with her passion."
Obsession is more like it, Keaton easily confesses.
As she told Preservation Magazine in 2003, "Houses enrich our lives with their history and the beauty of the architecture or their eccentricity, the details. You have to try to preserve some originals."
All may be second nature for an original like Keaton.
Now in her early 60s, Keaton has influenced a generation with her on- and off-screen style - the Annie Hall fashion, love affairs (real and cinematic) with Warren Beatty, Woody Allen and other leading men, and her recent unabashed middle-age romancing (including a nude scene) with Jack Nicholson. Never married, she is a single mom to two adopted children, now 12 and 6. Her previous books include a surprise - "Clown Paintings," a bittersweet look at clowns and comics.
Born and raised in California's Orange County, Keaton links her love affair with the Golden State's architecture to family trips to watch the swallows return to San Juan Capistrano and to stay in 1920's Santa Barbara Biltmore Hotel.
As she writes in the introduction to "California Romantica," "That was the summer it came to me, the idea that beauty could be felt from standing in the glow of afternoon light on the colonnade of a mission. That's when I came to understand that ache of romance that lived within the walls of our Spanish heritage.
"Romance has a lot to do with memories formed when you're young, where you went and what you saw, and that combines to form your idea of romance. Romance is about longing and that has sadness in it. It's not one flat thing. It's always light and shadow."
That interplay of bright and dark, interior and exterior, man-made and natural, is brilliantly captured in "California Romantica's" photography by Lisa Hardaway and Paul Hester. Rooms are sparely furnished intentionally, Keaton said, to focus attention on the architecture.
"I wanted you to see the clear, pure lines in the archways and the indoor-outdoor lifestyle, and the beauty and life that make these homes so magical," she said.
As D.J. Waldie points out, this architecture from the skilled hands of Lilian Rice, Richard Requa, Wallace Neff, George Washington Smith and others in the early 20th century melded Mediterranean styles into something uniquely Californian - red-tile roofs, airy courtyards, brilliant white stucco, rough-hewn beams, wrought iron, beamed ceilings, color-drenched tiles and, of course, arched windows that capture California sunshine and Pacific breezes.
"The golden light pouring into the houses they designed and their roomlike gardens and patios were part of a larger conception of life in (the American West)," he writes.
Keaton views their architectural achievements - the modern mix of adobe and Spanish flair - as "indigenous structures and very much representative of the dream of California, a place where everyone goes so their dreams will come true. It's why we called the book 'California Romantica.'
"There is nothing to compare to California. I was born here and I'm very passionate about this state."
LIFE WITH ARCHITECTURE
The residence Keaton now calls home was designed by Ralph C. Flewelling, a prominent Los Angeles architect best known for his Italian Renaissance Revival design of the Beverly Hills Post Office, now on the National Register of Historic Places.
"My house looks like a miniature mission, all colonnades and archways," she said. "I bought it once six years ago and got cold feet and then bought it again. In the meantime, I saw something else that had a lot more land. I restored it and have sold it. We've been living in a rental until the Flewelling was done."
This is the fourth vintage home Keaton has restored. Her earlier residences include a 1928 art deco home by Lloyd Wright, a 1926 Wallace Neff design and a 1920s "hacienda."
All, she says, are "eminently livable. There's a reason people are doing modern versions of old mansions. These homes are simple and soothing. They are a place to relax in a hectic life.
"Inside one, I can melt. I feel safe and protected. And the simplicity is divine."
Keaton passionately hopes others will follow her lead, updating rather than tearing down old homes.
"Today people want a kitchen-great room, which is really like a big living room. And they want a master bedroom-master bath suite. And when they look at something built in 1922, they say, 'Count me out,'" she says. "People are afraid of the work.
"But it's a question of readjusting how you approach the house. I've learned how to push the space around to make some rooms bigger. It just takes time."
A HUNTER'S FINDS
All 20 homes showcased in "California Romantica" - some remodeled and one new - were handpicked by Keaton.
"I was all over, scouting and taking pictures," she said. "It was the most exciting adventure - getting to see houses I'd never seen before and might never have gotten to see."
Included is a Rancho Santa Fe gem, the Black house, by Lilian Rice. Rice, the Ranch's resident architect during its early development, is described by Waldie in "California Romantica" as "an original. She was completely Californian in outlook, which to her meant subordination of structure to the landscape."
Rice was a protegee of Richard Requa, himself an apprentice of Irving Gill. A home by Requa - rich with Moroccan detail - built in 1926 on San Diego's Coronado Island, also is featured.
Five of "California Romantica's" homes are by George Washington Smith, an Easterner who settled in Montecito, and are synonymous with the red-tiled Spanish Colonial Revival architecture of that city and its neighbor Santa Barbara.
While she hesitates to pick a favorite, Keaton admits feeling she had "died and gone to heaven" in Casa Romantica, a 1927 hacienda on an ocean bluff in San Clemente designed by Norwegian Carl Lindbom.
"It is so astonishing," she continued. "Talk about endless colonnades. And it overlooks the ocean. I really liked that.
"I also liked the Bret Hofer house (a Gill-inspired contemporary in Laguna Beach) because it had some Hillside pottery that I wanted to steal."
Keaton's roving eyes and artistic spirit are on the watch for that - and more, like her next historic home remodeling project.
"I'm a hunter," she says. "I spend a little time in each and then move on. Each house has been so different, each with their own set of problems. They seem to have their own personalities.
"They aren't just structures; they are beings in a way. Each becomes like an extension of family. And I am very sad to leave them ... but I do."