Explore a geologic hodgepodge and an intriguing slot ravine at Anza-Borrego's Canyon Sin Nombre.

As daytime high temperatures in the desert sink from the 100s into the 90s during September, it becomes rationally conceivable to plan an overnight trip into Anza-Borrego's intriguing badlands. In fact, if you arrive in late afternoon and leave by midmorning the next day, your late-summer adventure need not be a terribly sweaty affair at all. The following tried-and-true trip, recommended for high-clearance, four-wheel-drive vehicles, takes you through the fault-churned Canyon Sin Nombre drainage, with an on-foot exploration of a narrow slot ravine. (Lacking the appropriate vehicle, you can still try hiking in and out of the canyon -- five miles round trip on a jeep trail -- but don't try this for another month or two until the weather cools sufficiently.)

From San Diego, drive 90 miles east to Ocotillo, exit the freeway, and head north on Highway S-2 for about 10 miles into Anza-Borrego Desert State Park. Watch for the green markers posted at mile intervals along the roadside. At mile 51.3, on the right, is the dirt road into Canyon Sin Nombre. Descend a briefly steep and sandy slope and continue toward the head of Canyon Sin Nombre.

The walls at the portal of the canyon are only a foretaste of the hodgepodge of shapes and colors to come. First, there are twisted, brown and gray layers of metamorphic rock, some shot through with narrow, light-colored igneous dikes. Just beyond, more igneous (granitic) rock is exposed. On the right (east) wall, about 0.3 mile farther, notice the spectacular, crumpled swirl of sedimentary layers. Movements along the Elsinore Fault in this area have produced horizontal displacements of up to 3 miles.

On farther the canyon broadens somewhat, and the walls are fashioned from mudstone and sandstone. At a point 1.3 miles into the canyon, a tributary cuts deeply into the clifflike left (west) wall. On foot, you can squeeze through the various narrow sections of this ravine, emerging in a sandy wash. Climb to the left as soon as you conveniently can to reach the brink of a cliff overlooking the sand-filled floor Canyon Sin Nombre.

Anza-Borrego Desert State Park's open-camping policy allows you to camp anywhere along the spacious wash of Canyon Sin Nombre -- though there are strict rules prohibiting ground fires. In September a light bedroll and sheet should suffice for sleeping arrangements, as the temperature may not sink much below 70 degrees. You are responsible for posting a parking permit ($5 per day, $50 yearly) whenever venturing off the park's paved roads. For more information, call Anza-Borrego at 760-767-4205 or 760-767-5311. Lastly, remember to take along plenty of drinking water, and travel safely with at least one other companion vehicle.