ON FAMILY VACATIONS WE have discovered the amazing diversity of Colorado's national parklands. In Rocky Mountain National Park, despite our older son suffering altitude sickness above treeline (11,000 feet), we oohed and aahed over the majestic panoramas and thrilling wildlife. At Bent's Old Fort National Historic Site, we toured the "Castle on the Plains." With its authentic furnishings and costumed staff', the reconstructed adobe trading post drew us into life along the Old Santa Fe Trail.

En route to Mesa Verde. America's premier sanctuary for cliff dwellings, we veered off southern Colorado's U.S. 160 to see the Great Sand Dunes. This short detour proved to be a fun opportunity to release the pent-up energy of long highway miles, but how did enormous dunes form in the shadow of snow-capped mountains? A rudimentary answer involves eroded particles being carried by streams off surrounding mountain ranges and swept by opposing winds into a corner of the high-altitude San Luis Valley.

Encompassing the tallest dunes in North America, the former national monument became Great Sand Dunes National Park & Preserve in 2004. It includes a new national wildlife refuge and an expanded national forest as neighbors. The dunes are now at the heart of one of the most diverse and unfragmented landscapes in Colorado, comprising hot desert sands, a tundra snowfield, forests, and wetlands. But all most visitors want to do is run, slide, and roll down the gigantic, curving sand mounds spread across a 30square-mile dunefield.

The Four Comers region, 200 miles farther west along U.S. 160, harbors a rich repository of remnants from prehistoric civilizations, with Mesa Verde National Park, established 1906, as its crown jewel. Long before European explorers arrived, ancient farmers settled here, their descendents staying on for 700 years. Early homes on mesa tops and canyon floors vanished long ago, but the elaborate masonry dwellings built into sheltered alcoves of canyon walls during the 1200s remain today as testaments to their societies.

Guided tours to many of the fragile cliff houses require tickets that limit group size. Time for taking several tours and exploring other ruins on your own can be maximized by ovemighting at Mesa Verde's Far View Lodge, especially since driving the long, curving road in and out of the park takes considerable time. And you can enjoy the park's 100-mile panoramas from the lodge's private balconies.

Not counting campgrounds, Mesa Verde is Colorado's only national park with sleeping accommodations. Lodging options outside the parks include vintage Victorian hotels and friendly bed and breakfasts in towns legendary for their ties to the Old West.

In places like Leadville, Cripple Creek, Central City, and Salida, you will find tours of old gold or silver mines, melodramas in restored opera houses, modern gambling halls, or chuck wagon suppers--maybe even a stagecoach fide. Outside the historic frontier town of Canon City, you will even find reputedly the world's highest suspension bridge spanning the Arkansas River's Royal Gorge, plus a chance to ride the state's only dinner train through the gorge. Colorado's storehouse of old forts, ghost towns, ranching homesteads, and hot springs offers plenty of enticements for stretching out the drive between parks.

Departing Mesa Verde, for instance, you might be diverted in Durango, Silverton, or Ouray along the exceptionally scenic U.S. 550. Summertime features excursions on the top-rated Durango & Silverton Narrow Gauge Railroad (continuously operated since 1882), professional rodeo in Durango, street gunfights in Silverton, and soaking pools fed by hot springs in Ouray.

Among unforgettable natural wonders, the shadowy gorge of the Gunnison River extends 48 miles--so deep, sheer, and narrow that little sunlight enters it. Black Canyon of the Gunnison National Park contains 14 of its deepest miles. Auto touring is the park's major activity, with strenuous inner-canyon hiking allowed by permit only. The South Rim Drive traverses seven miles (recommended time 2-3 hours) featuring 10 overlooks for heart-stopping peering into the almost-vertical drops of 2,000 feet.

Three reservoirs reaching nearly 40 miles along the continuing route of the Gunnison form the core of the adjoining Curecanti National Recreation Area, also under the care of the National Park Service. Named for a 19th century Ute Indian chief, Curecanti transformed the semi-arid area into a mecca for water sports, with fishing topping the list. A naturalist-led boat tour that skirts sheer canyon walls departs twice daily in the summer, but a one-mile hike to the boat dock involves 232 stairs. Visitors can also see a historic narrow-gauge train exhibit at a visitor center in the defunct town of Cimarron.

More spectacular scenery lies 70 miles northwest of Black Canyon of the Gunnison in Colorado's Grand Valley of the Colorado River, one of the last places settled by pioneers in the lower 48 and a major fruit producer. From the hub of Grand Junction, a dozen wineries invite wine-tasting tours and scenic drives cross the world's largest fiat-topped mountain (Grand Mesa) or highlight the area's paleontological sites.

Here the rugged terrain of the American West fills 32 square miles of Colorado National Monument, a plateau-and-canyon country of brilliant colors and fabulously eroded rock sculptures. This Colorado Plateau park echoes its famous counterparts in Utah and Arizona, but lies off the beaten path. The 23-mile Rim Rock Drive climbs from Grand Valley to the high country for panoramic landscapes of spires, domes, arches, pedestals, canyons, and the valley. Short trails lead to closer views of the dramatic monoliths.

In a region of dinosaur discoveries, Dinosaur National Monument safeguards more than 1,500 bones left uncovered and in place as a permanent dinosaur quarry exhibit that extends 20 miles into Utah. Its larger Colorado unit protects an extravagant expanse of stunning canyons, easily accessed on a 31-mile scenic drive (allow a minimum of four hours for the roundtrip). At the road's last overlook, you stand on fossils of ocean life at 2,700 feet above the Green River.

Extensive deposits of organic material that settled on an ancient lake bottom and got buried by volcanic ash prompted the creation of Florissant Fossil Beds National Monument, 35 miles west of Colorado Springs. This park is famous for fossilized insects--rarely entombed due to their fragility--and plant parts (leaves, twigs, cones, flowers). Discovered in the late 1800s and renowned for their variety, more than 50,000 specimens from the beds have been sent to museums and universities around the world. Visitors can follow short fossil-laden trails amid meadows and forested hills punctuated by petrified stumps of giant redwoods.

The 416 square miles of glacier-carved Rocky Mountain National Park captivates like few other places. Alpine meadows, sparkling lakes, wildflower extravaganzas, and the sound of rushing mountain waters provide endless delights on the sensational Trail Ridge Road, constructed in 1931 to gaze on "the whole sweep of the Rockies." Its winding 48 miles climb to a high point of 12,183 feet, where only superlatives exist. Allow at least a full day to savor the top-of-the-world vistas and lavish wildlife preserved at every elevation. IF YOU GO

FOR INFORMATION ON COLORADO ATTRACTIONS administered by the National Park Service, contact the following:

* Colorado Tourism Office. (800) COLORADO www.colorado.com.

* Bent's Old Fort National Historic Site, (719) 383-5010: www.nps.gov/beol.

* Black Canyon of the Gunnison National Park. (970) 641-2337: www.nps.gov/blca.

* Colorado National Monument. (970) 858-3617: www.nps.gov/colm.

* Curecanti National Recreation Area (970) 641-2337: www.nps.gov/cure.

* Dinosaur National Monument (970) 374-3000: www.nps.gov/dino.

* Florissant Fossil Beds National Monument, (719) 748-3253: www.nps.gov/fifo,

* Great Sand Dunes National Park & Preserve. (719) 378-6300: www.npsgov/grsa.

* Mesa Verde National Park. (970) 529-4465: www, nps.gov/meve.

* Rocky Mountain National Park. (970) 586-1206: www.nps,gov/romo.

RELATED ARTICLE: Gold, gambling, and nostalgia.

TRAVELERS DRAWN TO THE COLORADO ROCKIES FOR ITS GREAT natural attractions also find time to linger in historic mountain towns like Cripple Creek. Located on the western slopes of Pikes Peak, the colorful little community (pop. 584) is near Florissant Fossil Beds National Monument and about an hour's drive southwest of Colorado Springs.

Back in the 1890s, the Cripple Creek area, once a serene cattle ranch mushroomed into a gold camp of about 50,000 souls. Today the magnet is low-stakes gaming, introduced in 1991 to fund preservation of the business district's century-old buildings.