Lake Mead National Recreation Area, NV & AZ
Most visitors come here to take advantage of lakes Mead and Mohave. The former has become famous for its huge striped bass, and both lakes have abundant supplies of channel catfish, crappie, largemouth bass, and bluegill. But beyond the lakes, more than 87 percent of the 1.5-million-acre park is dedicated to protecting a vast area of the eastern Mojave Desert. And springtime is perfect for exploring the desert; in fact, the park service doesn’t recommend hiking here during summer, when temperatures can reach 125 degrees. There aren’t many established hiking trails, so be sure you can use a topo map if you venture into the backcountry.

Rock Climb in Joshua Tree National Park, CA
Back in the day, L.A. outdoorsy types overlooked deserts such as Joshua Tree. It was a little-visited monument that couldn’t match the locales in the High Sierras. But eventually word began to trickle out that the best winter rock climbing in the United States is here, on the warm monzogranite faces of Joshua Tree National Park. President Clinton signed the California Desert Protection Act in 1994 and turned Joshua Tree into a national park. But even with this added fanfare—and its proximity to LA and increasing popularity—the park has thankfully retained its low-key feel.

Big South Fork National River and Recreation Area, TN
Compared to neighboring Great Smoky Mountains National Park, Big South Fork is downright empty of crowds, meaning you’ve got 123,000 acres atop the Cumberland Plateau without having to jockey for position to indulge in one of its many active pursuits. Park visitors cite the natural arches and bridges, waterfalls and swimming holes, and more than 150 miles of hiking trails as prime reasons to enjoy the park, though some people get infinite enjoyment out of just pitching a tent and listening to all that all-natural silence. And then, there's the roaring Big South Fork itself, with more than 80 miles to paddle through a breathtaking gorge. In March, you might catch the last glimpses of snow or cascades of frozen waterfalls, but you’ll miss the winter hunters and the summer insects, which are obviously good things to avoid.

Kaibab National Forest, AZ
No forest in the southwestern United States can match the Kaibab National Forest's seamless fusion of canyon, desert, and mountain. And no other national forest is situated so preciously (and precariously) at the edge of the Grand Canyon. The Kaibab actually straddles the massive canyon, nudging up against both the north and south rim, and it serves as an excellent base camp for mountain-bike rides along the canyon rim and hiking expeditions into the labyrinth that lies below.

Natchez Trace Parkway, MS, AL, & TN
The 444-mile Natchez Trace Parkway recalls an ancient trail that connected southern portions of the Mississippi River to salt licks in today's central Tennessee. Experience this National Scenic Byway, which runs from Natchez to near Nashville in a car or RV, or, for the more adventuresome, on a bike. There are campsites along the entire route. Spring is an ideal time to explore the Trace, as temperatures start rising in the south and wildflowers line the route. There’s also opportunity for horseback riding, hiking, fishing, and attending special events that commemorate various aspects of U.S. culture.

Caribbean National Forest, Puerto Rico
Locally known as El Yunque, Puerto Rico's Caribbean National Forest boasts the distinction of being the only tropical rain forest in the U.S. National Forest System. It’s also the smallest of all the national forests, at 28,000 acres. But don’t be fooled; there’s big adventure waiting in this enclave perched just east of San Juan. Rain descends on the thickly vegetated hillsides in biblical proportions, and plant life is remarkably diverse. Beneath a towering canopy of trees, some as old as 1,000 years, fronds of giant ferns arch gracefully over the rainforest floor, bromeliads and epiphytes sprout from every nook and cranny of host trees, and rare orchids dangle a profusion of colorful blooms. March is the “dry” season, as much as there is such a thing. And remember, Americans still don’t need a passport to visit Puerto Rico.

Bandelier National Monument, NM
The dramatic sheer-walled canyon that defines the entrance to Bandelier offers immediate evidence that this is a special place. Carved hundreds of feet high on the rock walls are dramatic cliff dwellings that stand as a testament to the Anasazi, an ancient civilization that once ruled a swath of the Southwest. Bandelier covers nearly 50 square miles of steep, narrow canyons that flow from the 10,000-foot peaks of the Jemez Mountains to the Rio Grande River. It’s home to a wide variety of wildlife, including mountain lions, elk, black bear, and the protected Jemez Mountain Salamander. The main loop trail (1.2 miles), just behind the visitor center, provides access to some of the largest and most intriguing archeological sites in Bandelier. Camping and backpacking are also popular.

Congaree National Park, SC
You may know this park by its former name, the Congaree Swamp National Monument, a less-than-pleasant name for a truly delightful park. Ancient Redwoods of record size rule this park; take a walk among these trees to experience the beauty and tranquility of South Carolina’s only national park. The forest is home to hundreds of species of plants and animals, which you’ll no doubt become acquainted with, either on the 20 miles of hiking trails or while canoeing on Cedar Creek. If you plan to paddle, keep in mind that Congaree is BYOB—bring your own boat.

Capitol Reef National Park, UT
Capitol Reef is a land of twisting gorges, narrow slot canyons, and huge black boulders strewn about the red sandstone. But the defining feature of the park is undoubtedly the Waterpocket Fold, a nearly 100-mile-long warp in the Earth's crust that formed between 50 and 70 million years ago. As is typical in canyon country, summers can be brutally hot and bring flash floods. So visit the park in the spring, when the days are typically in the 60s. Do a day hike in the Fruita area, wet your line in the Fremont River, or head to the backcountry near Halls Creek. There’s even rock climbing for those who can’t resist a challenge on Wingate sandstone.

Redwood National and State Parks, CA
The majestic redwood trees are the primary reason most people visit the park, but the coast redwood ecosystem hosts an amazing diversity of life. Keep your eyes peeled for small critters such as banana slugs and seas anemones, and for much bigger inhabitants such as gray whales and black bears. There are equally diverse ways to experience the park. Take a scenic drive along the coast, or get a closer look on horseback. Better yet, take to the water on a kayak. The park has some 200 miles of hiking trails and even allows biking in a few select backcountry spots (rare for a national park). Native Americans have long thrived in this part of California; the visitor center has lots of information about the history and culture of the area.