One piece of advice for road-tripping through the Southwest: don't try to cover too much ground. You're talking about a huge area of land, and if you try to cram in too many destinations, you won't have the time to appreciate any. Drive east to Utah, where you can find varied terrain and a number of national parks and monuments. Here's my suggested road trip.
Help Me Plan My Southwestern Road Trip: Vegas to Zion
I'd tell you to wake up early, but you're starting in Vegas, so forget that. Just get up by noon and drive the 160 miles on I-15 to Zion National Park in Utah and its slot canyons, arches, and massive sandstone cliffs. (Skip Lake Mead: it's artificial, and not worth the hype.) Turn off the Interstate at Lake George, take Route 9 to the park's South Entrance, and unload at the Watchman Campground ($16 per night). From the nearby visitor's center, you can catch shuttle buses to almost anywhere in the park.
Help Me Plan My Southwestern Road Trip: Zion National Park
With so much to see and do in Zion, you're not driving anywhere today. There are too many options to list here, but my suggestion would be to make the five-mile out-and-back hike up to Angel's Landing, a 1,500-foot rock formation that juts out above the canyon. The switchbacking trail near the end is slow going, but it's worth it for the bird's-eye view from the summit.
Help Me Plan My Southwestern Road Trip: Bryce Canyon National Park
Break camp early and drive two hours northeast on Route 89 to Bryce Canyon National Park, a massive natural amphitheater famous for its multicolored rock spires. Grab a site at the park's North Campground ($18 per night), then strike out on the 8.5-mile Riggs Spring Loop Trail, which descends 2,200 feet through aspen and evergreens and affords broad views of the spires along the way.
Help Me Plan My Southwestern Road Trip: Capitol Reef National Park
Take your time driving Route 12, maybe the prettiest stretch of asphalt in America. The road wanders across the northern edge of Grand Staircase-Escalante National Monument, through the Dixie National Forest, and over 11,000-foot Boulder Mountain, home to some of the finest fly fishing in the Southwest. After about 115 miles, you'll hit your next destination, Capitol Reef National Park. This 242,000-acre collection of bleached sandstone domes and cliffs overlooking the Fremont River is often overshadowed by its larger, more famous neighbors, like Bryce Canyon and Canyonlands. That's good for you, because the park is seldom crowded. Grab a site at Fruita Campground ($10 per night).
Help Me Plan My Southwestern Road Trip: Fishlake National Forest
Leave Capitol Reef and drive two hours east to the 1.5-million-acre Fishlake National Forest, a high-alpine plateau filled with peaks and streams. What you can do here depends on the size of the snowpack. The trout fishing on Fish Lake, Utah's largest freshwater alpine lake, is nearly unsurpassed in the West, and the 25-mile Mytoge Mountain Trail that rings its shores attracts mountain bikers from around the country. If the spring thaw hasn't happened yet, you might be able to take some turns on the 42 runs at Eagle Point ski resort. Stay at homey Moore's Old Pine Inn in Marysville. The flag-draped Betsy Ross room starts at $65 per night.
Help Me Plan My Southwestern Road Trip: Cedar Breaks National Monument
In the morning, drive south on Route 89 and cut across the Tushar Mountains, the third-highest range in Utah, on State Route 153. You'll then take I-15 south for about an hour, until you arrive at Cedar Breaks National Monument. This rocky, three-mile-wide and 2,000-foot-deep hoodoo-filled amphitheater looks almost like a smaller Bryce Canyon, and doesn't open until the snow melts in mid-may. In the summer, stay at Point Supreme Campground for $14 per night, no reservations necessary. If you want something less primitive, you can spend the night at nearby Brian Head Resort ($225 per night).
Now it's back to Vegas, only three hours down I-15.