Almost everyone who lives in the San Francisco Bay Area has passed through Yerba Buena Island, but few have ever set foot on it. Hundreds of thousands of cars pass daily through the tunnel that runs through it, connecting the two spans of the San Francisco-Oakland Bay Bridge. As we cross the bridge we see taillights, headlights, city skylines, the bay's glittering waters, the tunnel lights. We pass through Yerba Buena Island without seeing it.

To be sure, this rocky bay island has been occupied by the military and virtually off-limits to the public since 1867. No "public access" signs show the way. Along with its man-made neighbor, Treasure Island, it will be turned over to the City and County of San Francisco within the next few years. But you can explore Yerba Buena now--and if you're interested in native plants, you will discover treasures.

I was once among those who had never given much thought to Yerba Buena Island. As a biological consultant surveying plant communities around the region, I often crossed the Bay Bridge on my way to other destinations. Out of the car window I caught glimpses of little more than invasive exotic plants, mainly eucalyptus trees and French broom, and with disdain turned my attention elsewhere. But in 1996 I was asked to conduct a botanical study of the island as part of the U.S. Navy's base-closure environmental study. To my surprise, I discovered remarkable remnants of the island's indigenous flora. Over the course of a two-year study, I became, and remain, obsessed with exploring these remnants, and with learning more about what I soon realized was the island's fascinating history.

If you can tune out the incessant roar of the traffic on the Bay Bridge, a visit to Yerba Buena Island can be a trip back in time. With a little imagination, it's not too difficult to picture the island as it once appeared: a grassy knoll covered with wildflowers, with oaks on its north side and fragrant sage scrub along the bluff tops. For optimal enjoyment, however, I strongly recommend exploring it as part of a group tour or work party (see sidebar).

The acquisition of Yerba Buena Island by the City of San Francisco offers a rare opportunity to preserve natural resources that have been virtually hidden away at the heart of a large metropolitan area. If development there is sensitive to these little niches of remaining habitat, both residents and visitors will be able to enjoy the unique sense of place they provide long into the future.

Mike Wood runs a small environmental consulting firm in Walnut Creek and performs biological surveys and impact analyses throughout California. A board member of the Yerba Buena chapter of the California Native Plant Society since 1994, he writes the regular feature "Focus on Rarities" for the chapter newsletter.

This article is greatly abridged. For the complete story, see the print edition of Coast & Ocean.