Descanso Is Getting a New Look : Renovation: A waterfall, an expanded lake and a pedestrian path are in the works for the gardens in La Canada Flintridge.

To the average observer, a new waterfall at Descanso Gardens appears to be a natural rock formation with water cascading down from a lake just above.

But the waterfall is actually a sophisticated construction project: The water recirculates through a plumbing system separate from the lake, and 140 tons of artificial rock made out of concrete is wedged inconspicuously among 120 tons of genuine granite boulders.

Granite boulders aren’t always the right size or shape, project supervisor Bill Beggs said, and some of them would have been too heavy to place in precarious positions near the falls.

So workers from Anaheim-based Rock Formations built concrete rock casings into the hillside as well as a number of artificial boulders to achieve the look that Glendale architects Larry Moss & Associates wanted, Rock Formations owner Bruce Riley said.

The artificial rocks were treated with paint to make them look natural, and a treated substance called “soil cement” makes the bottom of the falls look natural, he said.

Completion of the falls marks the halfway point of a $350,000 lake renovation project funded mainly by the Descanso Gardens Guild. Descanso also received a $70,000 grant from Los Angeles County for the project, guild President Gail Boatwright said.

Construction is still under way on the second part of the project, the large lake at the top of the falls, Beggs said. The lake, designed to be a bird sanctuary, is scheduled for completion in November, before the bird migration season, he said.

Two smaller lakes were combined to create the 1.5-acre lake, he said. It will feature tiny islands where birds can nest and marshes where they can hide from predators, he said.

Coyotes have preyed upon birds in the past, killing many nestlings, he said. More than 130 varieties of birds frequent the gardens in La Canada Flintridge, according to a checklist prepared by the county Department of Arboreta and Botanic Gardens.

The main county arboretum in Arcadia is donating tule, or long reeds, to landscape the edges of the lake, Boatwright said. Native California plants, Australian shrubs and two large willows will also border the new lake, she said.

Once the project is complete, visitors will be able to follow a path that will wrap around the lake and extend over the waterfall, he said.