The Scripps Coastal Reserve, managed by the University of California Natural Reserve System, includes a small, undeveloped mesa overlooking the ocean, steep canyons to either side, and an underwater preserve beneath Scripps Pier. Up on the finger-like mesa, you can get a good inkling of the earlier character of the La Jolla-Del Mar coastline -- a treeless, scrub-covered landscape falling steeply away to the sand and the surf. No dwellings were ever constructed on this mesa top, though a half-century of farming and cattle grazing greatly altered the topography, soil, and vegetation present there now. Today, biologists are trying to return the mesa-top to its original ecological condition.

You and your visiting relatives and friends should check out the reserve's Biodiversity Trail, one of La Jolla's unsung outdoor attractions. You'll find the trailhead between two houses on La Jolla Farms Road, 0.1 mile west of La Jolla Shores Drive. There's limited curbside parking nearby. The one-half-mile-long trail circles the rim of the mesa and lets you gaze over miles of spectacular coastline both north and south. So commanding is the view at the western edge that gun emplacements were set up there during World War II to help defend San Diego from anticipated attacks by sea.

At the trailhead you can borrow a self-guiding booklet that has a lot to say about the reserve's diverse array of indigenous and nonnative plants and animals. Over 200 different kinds of plants, nearly 100 birds, and a dozen mammals have been identified within the boundaries of this small reserve. You'll be surprised to learn, for example, that roughly 1000 specimens of the increasingly rare coast barrel cactus have been counted in the reserve.

When crystalline skies prevail, as they often do in late fall and winter, a late-afternoon vigil on the mesa may bring the spectacle of the sun's reddened, ovoid disk sinking quietly over the distant, watery horizon. Also, for some weeks to come, you can hunt, with binoculars in hand, for visible traces of the southward migrating gray whales.