As one of the richest wetland areas Southern California, the San Joaquin Wildlife Sanctuary offers an uncommon opportunity to come in contact with a natural ecosystem seemingly plunked down in the midst of Orange County's airport/urban district. Amid willows, cattails, and tules, you can spy on ducks, geese, and shorebirds, listen to bullfrog choruses, and perhaps even spot pond turtles sunning themselves on protruding limbs. You can thrill to the graceful antics of herons and egrets, and the soaring flights of marsh hawks.

Make no mistake, the entire 300-acre spread, in its present incarnation, is essentially an urban park, planted densely with native trees and shrubs and irrigated with water from holding ponds that are part of a state-of-the-art wastewater treatment plant. Starting in the 1990s, the Irvine Ranch Water District, with the support of the Irvine Company and the Sea and Sage chapter of the Audubon Society, began an ambitious project to transform the once-neglected and raw-looking property into a naturalistic landscape typical of Orange County's original lowland and upland habitats. That effort has resulted in a tightly nested, ten-mile system of wide, smooth, wheelchair-accessible trails, restrooms and resting benches galore, and most importantly a first-class habitat for birds.

Audubon volunteers have installed dozens of nestboxes throughout the sanctuary to attract cavity-nesting birds, and they conduct a monthly bird census that has resulted in sightings of nearly 300 species of birds to date.

A good way to enter the sanctuary is to park along the roadway known as Riparian View, south of Michelson Drive in Irvine. There are two parking lots/trailheads here, open dawn to dusk, plus a one-page trail map that you can take with you. The map details several signed routes pieced together out of the bewildering maze of wide trails and levee-top roads that reach every corner of the sanctuary.

The southern of the two trailheads marks the beginning of the 0.8-mile-long Tree Hill Trail, perhaps the best route for getting an overview of what the place has to offer. On it, you first visit Tree Hill, where African acacias and other exotic trees dot the top of a small knoll -- a landscape demonstration project begun by the water district on Earth Day 1990. You then descend past planted pines, sycamores, and cottonwoods and through a meticulously tended facsimile of sage-scrub and chaparral habitat. Curling around the perimeter of the water-treatment plant, you find yourself on the levee of one of the several rectangular ponds, which are actually settling basins.

The Tree Hill Trail "route" ends halfway around the first settling basin, but that's just the perfect place to start circling one or more of the five natural-looking ponds (designated Ponds 1 through 5 on the trail map), which offer excellent opportunities for serendipitous discoveries of birds and other wildlife.

The San Joaquin Wildlife Sanctuary is clearly a place for wandering and quiet observation, rather than goal-oriented hiking. In fact, the whole place was carefully designed with berms, fences, and landscaping designed to screen out sight and sound of the surrounding city and its traffic.