We're still crossing the American heartland, to sample the top scenic road treks in America. Here are three more as suggested by Sheila Resari of www.Gorp.com.

ZION NATIONAL PARK SCENIC BYWAY, UTAH

To view this geological wonderland, head east from St. George to Zion National Park and Zion Canyon, the Utah rock carved into fantastic shapes by erosion and richly colored by iron and manganese. Inside the canyon, a free bus — mandatory to combat overuse and overcrowding of the park's most popular destination — shuttles down Zion Canyon Scenic Drive. The North Fork of the Virgin River cut Zion's soft sandstone into the canyon it is today, with 2,000- and 3,000-foot-high cliffs. At the drive's end, visitors can hike the Narrows — a 20-foot-wide passage between the cliffs — by wading through the river.

Heading east from the canyon, the byway switchbacks up steep plateaus and passes by the Great Arch, cut from the sandstone by erosion. The road continues through the mountainside via the Zion-Mount Carmel Tunnel; at points along the tunnel, natural windows in the rock allow drivers to peer out across the canyon. After the tunnel the highway runs past the Canyon Overlook trailhead and the Pine Creek narrows — long ropes and climbing experience are required to explore this deep slot canyon. From here to Mount Carmel Junction, the highway curves past sand dunes, slickrock, and the crisscrossed sandstone of Checkerboard Mesa.

Route: East from St. George to Zion National Park. Guided bus ride (closed to all private vehicles in summer) through Zion Canyon. Drive continues to Mount Carmel Junction. Length: 54 miles (half a day). Season: April through October. Features and activities: Hiking past waterfalls and hanging gardens on the Emerald Pools trail; climbing up to 5,990-foot-high Angels Landing (not for acrophobes!); riding a horse or mule through the canyon; and viewing more than 800 native species of plant and wildlife.

CUSTER SCENIC BYWAY, SOUTH DAKOTA

Although dominated by ponderosa pine, the Black Hills — known to the Lakota Sioux as Paha Sapa — are home to a combination of plant life from the Rocky Mountains, the Great Plains, and the northern boreal and eastern deciduous forests. Custer Scenic Byway cuts through the southwestern corner of South Dakota, a state characterized by the grassy, rolling hills of the Great Plains.

Before heading north, travelers can go underground, through 70 miles of winding passageways amidst the incredible limestone formations of Wind Cave National Park. Further along the byway, the Rankin Ridge National Recreation Trail — a one-mile, self-guided nature trail — explores the virtues of the park aboveground. The Black Hills are a climber's mecca: formerly occupied by 14,000-foot peaks, the land still reflects that rugged height in amazing spires and outcroppings found along the Needles Highway. From the drive's end at Sylvan Lake, hiking trails ascend Harney Peak — the highest American mountain east of the Rockies — for a grand view of the Black Hills and nearby Mount Rushmore.

Route: From Wind Cave National Park through Custer State Park to Sylvan Lake in Black Hills National Forest. Length: 33 miles (1 1/2 hours). Season: Spring through fall. Features and activities: Wildlife viewing at the Prairie Dog Pullout, a 360-degree vista from the Mount Coolidge fire tower, and wildlife (bison, elk, pronghorn, burros) and wildflower viewing in Custer State Park.

NORTH SHORE DRIVE, MINNESOTA

The North Shore Drive runs along the wild Northwoods, flanked by Lake Superior and the aptly named, glacier-carved Sawtooth Mountains. The rocky North Shore, the product of volcanic flow and glacial ice, is the Minnesota side of the world's largest freshwater lake.

The 100-foot cascade of Gooseberry River into Lake Superior is the highlight of Gooseberry Falls State Park, one of eight along the drive. The route also runs through Superior National Forest — the only place in the continental United States where the boreal landscape still flourishes. From the resort town/artist colony of Grand Marais, hikers, dogsledders, and cross-country skiers can hit the Gunflint Trail, a gateway to the Boundary Waters Canoe Area Wilderness.

Grand Portage, the last town before the Canadian border and the hub of the 17th- and 18th-century fur trade, was so named for the 8.5-mile trek voyageurs and Indians had to make between Lake Superior and Fort Charlotte. A few miles farther, Mount Josephine offers a 1,348-foot view of Lake Superior, the peninsula and nearby islands, as well as beautiful Teal Lake.

Route: Duluth to Grand Portage along Lake Superior. Length: 150 miles (three hours). Season: Spring through fall. Features and activities: Birding and blueberry picking at Palisade Head, hiking along Temperance River and the Superior Hiking Trail, climbing Carlton Peak, and wildlife viewing in Superior National Forest (and by the "Moose Area" sign at the second Route 14 junction).