Sunny winter days are perfect for exploring San Diego County's population-equivalent of Saudi Arabia's Ar Rab al Khali, or "Empty Quarter." Virtually no one lives in the county's northeasternmost 100 square miles, an arid region of fault-dropped basins and sinuous ravines bisected by the mile-plus-high summits of the Santa Rosa Mountains. More than a century ago the scene here was more lively -- at least in winter and early spring -- when bands of migrating Cahuilla Indians settled in at lower elevations to stay relatively warm and exploit the growth and ripening of the native desert vegetation.

Today, Anza-Borrego Desert State Park (phone 760-767-4205) has jurisdiction over the area -- though you should not interpret the word "park" to mean a recreational area that's easy to get into, either by car or by foot.

The following long, looping walk -- ten miles over gently rising and then gently falling terrain -- can be a good introduction for experienced hikers who appreciate solitude and profound silence. Don't forget to pack along essentials such as plenty of water, food, extra clothing, and maps and skills to navigate the convoluted terrain.

At mile 26.7 according to mile markers on Highway S-22 (north and east of Borrego Springs), turn north on Clark's Well Road. Pavement soon ends and you continue driving on dirt, bearing left at 1.5 miles onto Rockhouse Truck Trail. In a short while you skirt the west edge of the normally dry and salt-encrusted Clark Lake. (When wet, after heavy rain, a short section of the road ahead can become muddy and impassable.) After nine miles of dirt-road travel in all, you arrive at the junction of primitive roads going into Butler and Rockhouse canyons. Park near here.

On foot, follow the Rockhouse "road," a rough jeep track at this point, north into the broad, dry wash of Rockhouse Canyon. The San Jacinto Fault (a San Andreas splinter) parallels this section of canyon. At about three miles, there is a road-closure sign. Continue another mile to Hidden Spring -- more of a seep than a spring -- identified by a sign on the left. The small basin there may hold a gallon or two of insect-infested, nonpotable water.

From the spring itself, a path past some mesquite bushes will guide you to a deeply worn, eroded trail slanting south and upward across a 200-foot-high bluff. Just over the top, on the eastern edge of Jackass Flat, are the remains of a Cahuilla Indian village occupied as recently as the late 1800s. You may chance upon some old fire pits, pieces of pottery, and flakes of a metamorphic rock known as wonderstone, which was once used for stone tools. Do not remove any items of any kind (a state-park rule), no matter how small they are.

Now head west about a mile to the head of Butler Canyon, which carries water from Jackass Flat south. Follow Butler Canyon, assisted by gravity all the while, as it descends for four miles through a sinuous gorge carved out of gleaming granitic rock -- a rewarding concluding segment of the hike. Beyond the mouth of this gorge you'll come upon wheel tracks that lead right back to your parked car.

This article contains information about a publicly owned recreation or wilderness area. Trails and pathways are not necessarily marked. Conditions can change rapidly. Hikers should be properly equipped and have safety and navigational skills. The Reader and Jerry Schad assume no responsibility for any adverse experience.