There's still much more to come in the months ahead as the Children's Museum of Sonoma County gets ready to open its gates to the public and set young minds loose on the world of creative exploration.

But it's already pretty hard to resist the urge to splash through the cascading waters out front or clamber over the boulders along the shore of a realistic river now under construction.

A full-scale mock-up of the Sonoma County Main Street indoors proves equally alluring to the child in anyone — full of cubbyholes and passageways, garrets and a lattice-like structure that eventually will be part of a treehouse with a spiral slide and pulley system for collaborative play.

Barely even a dream eight years ago, the children's museum set to open next year in its permanent digs on West Steele Lane in Santa Rosa finally feels real, with construction under way and the first of its installations beginning to take shape.

Though $1 million still needs to be raised toward its $8.3 million cost, it's possible now to envision how the museum's colorful schematics will translate into three-dimensional, interactive exhibits full of motion, energy and intrigue.

Construction started several months ago — mostly underground electrical work, trenching and storm drain installation. Earlier this month, two representatives from an Illinois company specializing in naturalistic water features joined up with a crew of local contractors to build a 65-foot representation of the Russian River in front of the museum.

Framed by more than 100 tons of boulder and other rock, the river includes a headwaters, waterfall and wetland area in which native Russian River plants will be grown. The water — which circulates at a rate of 20,000 gallons an hour — will be cleaned through a natural filtration process that uses enzymes, beneficial bacteria and layered pebbles.

Several bubbling boulders perched atop a gravel bed that kids will be able to play on help oxygenate the water and provide a fun place to play.

"The whole idea behind this is, to me, the local environment," said Ed Beaulieu, who helped design the river on behalf of Aquascape, a St. Charles, Ill., company that donated a significant portion of the work.

For Collette Michaud, the museum's founder and chief executive, the river installation was a landmark moment.

"It's really the first exhibit that you can really see and touch," she said.

The river, located at the center of the 35,000-square-foot outdoor exhibit area known as Mary's Garden, is "kind of the hole in the doughnut, because everything is kind of keyed off of it," Michaud said.

Curving concrete seating walls are coming next, along with plantings and water-play installations being built off-site. Crawlable, climbable exhibits built on the theme of the metamorphosis of a butterfly — or mariposa, in Spanish, which gives the garden its name — will be added, as well, all in time for a March opening of the outdoor exhibits.

Nearby, carpenters are assembling a 1,000-foot structure for use as an art studio and party/event center. It will be erected on the foundation of an old farm house that was to be renovated until dry rot was discovered.

Both the outdoor garden and the party/art building are expected to be completed early next year, just as construction gets under way on the indoor Science and Imagination Gallery, which includes a Victorian Main Street, a large "hardware store" with tools and supplies for building things, a huge floor-to-ceiling robot, and a health and dental lab, all outfitted with interactive exhibits. A live beehive will be part of the gallery, as well.