When everything is in bloom in the spring, "It's breathtaking," said Hamby.
"In March 2007 we cleared the hillside except for the apple, pear and plum trees," she recalled. On the south side she left four oaks - one estimated to be 300 years old - in the part of her yard she describes as "volunteer," meaning the birds drop the seeds and the plants grow without fertilizer or watering.
Hamby, a residential architect, had a large pond - 35 feet by 40 feet - installed toward the bottom of her lot with an island and a bridge. Two streams cascade into it, a total of 13 waterfalls. Then she hooked up with landscape artist Kristin Yanker-Hansen, who designed the paths and the terraced gardens.
"All I did was approve - wholeheartedly," Hamby said. "For three whole days we visited wholesale nurseries, as far as Santa Cruz and Monterey."
Two pairs of gates that mirror the design details in the arbors above and are reminiscent of Tobi gates lead to different sections of the yard. The first gate, at the end of the driveway, opens onto a stunning view of Mount Diablo directly across the valley. Near the house are several decks, places to sit and feast your eyes on the distant view or the profusion of garden color and the sound of splashing water at your feet.
Hamby specified that the steps down the hillside be wide and deep to make the paths easier to traverse. As she walked up and down talking about her garden plans for this spring, she pointed out plants and features, and tugged at a weed here and there. "I'm a compulsive weed puller," she said with a laugh.
She also keeps an eye out for signs of her nemeses - the gophers, skunks, possums and the raccoons, which were responsible for the demise of 150 mosquito fish and six koi that once swam in her pond. An eight-foot fence keeps out the deer.
Each retaining wall is at eye level with the path in front of it for easier appreciation - and maintenance - of its foliage. The paths cross the streams and Hamby demonstrated how easy and delightful it is to put a hand under the tumbling water.
The paths lead to a deck at the bottom of the yard, a peaceful gazebo, a place to sit and to gaze at the mesmerizing streams. A stone walkway leads from there along the pond to the shady volunteer part of the garden and up to a more formal plot where Hamby grows vegetables. Along the house are rows of rose bushes - and a stone with carved words: "Grow dammit."
"You should have humor in your garden," Hamby noted in her cheery Massachusetts accent.
That side yard leads through an arbor into the enclosure that approaches the front door, a private garden with a lawn and high fences covered with vegetation, and a fountain sculpture. On the other side are the gates, leading back to the driveway and the real world.
When the Hambys bought their home 42 years ago, it was surrounded by walnut orchards.
"We bought it because it was a view lot," Jan recalled.
Their three daughters used to slide down the hill on saucers, play baseball on the lower level, and have sleep-outs. They also enjoyed tire swings hanging from the old oak tree.
Now a beach of large pebbles leads into the pond, and Hamby says her grandchildren enjoy cruising a remote control boat around the water and under the bridge.
Some plants remain from the original garden. A primrose in the side yard trumpets its cheery colors in the shadow of a daffodil.
In the intervening decades, Jan Hamby, who is the president of two garden clubs, has added myriad plants and flowers, experimented, worked with her landscape artist and her gardeners, Juan Rodriguez, and derived much pleasure from her yard.
Hamby's domain will be part of the AAUW Garden Tour on May 8-9 for the first time.
"Last year I had five different tours," she said.
Now she is looking forward to sharing her hillside paradise with those touring in May.
"I'll be out there talking to everyone," she said.
Visit the gardens