The San Joaquin Marsh is one of the more improbable things you'll find in coastal Southern California: a large, working freshwater marsh tucked between freeways and office parks. The sanctuary covers roughly 300 acres and was constructed on former agricultural land — not a relic of the original landscape, but a genuinely functioning wetland that has been reclaimed from the development that surrounds it on all sides.
Over 200 bird species have been recorded here, including herons, egrets, coots, various ducks, and raptors. The Audubon Society manages the reserve jointly with the Irvine Ranch Water District, which continues to use some of the wetland cells for water treatment — an unglamorous arrangement that nevertheless works well for the birds. Entry is free. The trails are flat and easy, suitable for all ages and fitness levels. Go in early morning if you can: the light is better, the birds are more active, and you will have the paths largely to yourself before the sun gets high. Weekday mornings in particular feel genuinely peaceful given how close you are to several million other people.