El Pinacate

The somewhat difficult trip to El Pinacate is also one of the region's most rewarding. The reserve, midway between Puerto Peñasco and the Arizona border, is famous for volcanic rock formations and thousands of moonlike craters. Highlights include 4,000-foot-high Santa Clara peak, and the mile-wide El Elegante crater, created by a giant steam eruption 150,000 years ago.

With the addition of a solar-powered visitor center, which opened in 2009, exploring the area isn't quite as daunting. But you'll still need to plan ahead, bringing your own water, food, and extra gasoline. A high-clearance four-wheel-drive vehicle is also strongly advised. Since an unpopulated stretch of desert is a great place for drug trafficking and illegal border crossings, use common sense. Lastly, be mindful of the heat—summer temperatures can be blistering. The best time to visit is between November and March.

All visitors must register at the park entrance, where a ranger's station provides informative tips for visitors. For current park information, contact the International Sonoran Desert Alliance in Ajo, Arizona, at 520/387–6823 in U.S. Hwy. 8, Km 51, Esperanza, near Ejido Nayarit, Puerto Peñasco, Sonora, 83550. 638/384–9007. $3. Daily 9–5.

Excellent naturalist-led tours can also be arranged through La Ruta de Sonora in Tucson. 520/886–6555 in U.S. www.laruta.org.