Greg Gaar: Laguna Honda Canyon ­ An Unknown Treasure

Thousands of people drive through Laguna Honda Canyon every day, but how many notice the vast open space that surrounds them?

Laguna Honda Canyon stretches from the Garden for the Environment, at Seventh Avenue and Lawton Street, south between the steep slopes of Mt. Sutro and Sunset Heights and levels out near Forest Hill Station. According to Harold Gilliam's book, "The Natural World of San Francisco," Laguna Honda Canyon was carved by a river flowing for millions of years.

Old maps and photographs show that there were two lakes in the canyon ­ Laguna Honda, which was converted into a reservoir in 1863, and the "Waste Pond" (filled in by 1920), situated near the present pumpkin and Christmas tree lot at 7th and Lawton. The SF Unified School District owns the property.

The river flowed into many of the 14 native lakes that were filled-in when Golden Gate Park was developed.

Laguna Honda Canyon is ecologically unique because numerous native plant communities converge there ­ Dune Scrub, North Coastal Scrub, Oak Woodland, Coastal Prairie and Riparian.

The sand dunes in the canyon ­ now stabilized by exotic and native vegetation and cut off from its ocean source ­ cover the western slopes. As sea levels rose 350 feet over the last 12,000 years, sand drifted relentlessly inland, flowing over Golden Gate Heights and Sunset Heights and into the canyon, where the dunes naturally dammed the river and formed the two lakes.

A diverse North Coastal Scrub community is still very intact on the west slope of Mt. Sutro, above the Laguna Honda Reservoir. This 20-acre site might be the finest native plant community in San Francisco. The rare San Francisco Gumplant populates the slope, along with buckwheat, Yerba Buena, Iris and Indian Paintbrush. Garter and gopher snakes, western fence lizards, skunks, raccoons and opossums live under the dense thickets of coyote bush, sagebrush and monkey flower. The habitat is rich with butterflies, songbirds, kestrels and hawks.

This incredible remnant of our natural heritage is the only part of Mt. Sutro where Adolph Sutro didn't plant trees at the turn of the 20th century. Otherwise, this rich habitat would have been replaced by eucalyptus trees and lost forever.

Last year, in order to eliminate homeless campsites, the SF Water Department released 500 goats to defoliate the rare plant community. There was no public notice, no hearing and no environmental evaluation. Fortunately, environmental activists were able to stop the destruction. If this living museum of our natural heritage is going to survive for future generations of people and wildlife as mandated by the city's General Plan, the land should be transferred to the SF Recreation and Park Department so the Natural Areas Program can properly manage it.

Some of the riparian habitat that carved the canyon still survives. White Crane Spring flows down the west side of Mt. Sutro above the community garden at Moraga Street. Lake Honda, surrounded by willows and cat tails, is used by herons, egrets and other waterfowl. An aquifer flows under the canyon and into the arboretum, where the water is pumped to the summit of Strawberry Hill and used for irrigating Golden Gate Park.

Large coast live oak and toyons still grow on the sheltered slopes on both sides of the canyon. The oaks behind the homes on Seventh Avenue are hundreds of years old, but they are being killed by climbing English and cape ivy.

The coastal prairie grassland that beautified the rolling hills from Twin Peaks to Laguna Honda Hospital (originally the almshouse) is all but gone in the canyon. One of the last slopes covered with wildflowers, south of Clarendon Avenue, was plowed into a victory garden during World War II and few of the native plants returned.

Laguna Honda Canyon has existed for millions of years as a natural wonder. But the impacts of urbanization ­ traffic, weeds, homeless camps and mismanagement) will eventually destroy the bio-diversity of the canyon.

Step one in preservation is to learn that the canyon exists. Step two is to manage it appropriately. Can we succeed?

Greg Gaar is a local historian and member of the Native Plant Society.