In Montana and Wyoming, the earth seems to have turned itself inside out, its hot insides leaking into hot springs and geysers, its bony spine thrust right through the skin of the continent to form the Continental Divide, making it a geologist's dream. And to a biologist it's heaven, one of the last regions in the United States with enough open space for animals like elk and grizzly bears to roam free.

Plains, basin, and range alternate in this high-altitude environment that is in large part defined by its extremes of weather and climate. These changing landscapes make Montana and Wyoming two of the best vacation spots in the country for travelers who like their scenery dynamic and dramatic.

The western side of both states is mountainous, dragging moisture from the clouds moving west to east and storing it in snowpack and alpine lakes. Because the ridge of the Rockies wrings moisture from the atmosphere, you find deeper, denser forest extending far to the west, while on the east side, the lodgepole pine, spruce, and fir forests give way to the Great Plains, a vast, flat land characterized by sagebrush, native grasses, and cottonwood-lined river bottoms.

But a lot of the landscape dates back more than 100 million years to when the collision of tectonic plates buckled the earth's crust and thrust these mountains upward. Later, glaciers (of which some vestiges remain) carved the canyons. The tallest peaks in Wyoming are located within the Wind River Range, which rises from the high plains of South Pass and runs northwest to the Yellowstone Plateau. Nine of the peaks in the Winds have elevations over 13,000 feet; Gannett Peak, at 13,785 feet, is the highest in the state. Several other mountain ranges are found to the south of Yellowstone -- including the Absarokas and the stunning Tetons -- and from Yellowstone north into Montana run other dramatic ranges, including the Gallatin, Madison, Mission, Bitterroot, Cabinet, and Beartooth, where you'll find Montana's highest point, Granite Peak, at 12,799 feet.

The Continental Divide enters Montana from Canada and traces a snaking path through the two states. Both Montana and Wyoming have rivers flowing west to the Pacific and east to the Atlantic.

Here you'll also find the headwaters of major river systems -- the Flathead and Clark Fork heading west into the Columbia from Montana, along with the Snake from Wyoming; the Yellowstone, North Platte, and Madison joining the Missouri bound east; and the Green from Wyoming emptying into the Colorado heading south. These rivers are the lifeblood of the region, supplying irrigation, fisheries, and power from dams. Montana also boasts the country's largest freshwater body of water west of the Mississippi River: Flathead Lake. Yellowstone and Jackson lakes are Wyoming's two largest natural bodies of water.

Montana is the greener of these two states, with more abundant alpine wilderness and bigger rivers. Wyoming, however, has been dealt a more interesting hand of natural wonders: waterfalls, geysers, and other geothermal oddities at Yellowstone; as well as the natural landmark of clustered rock columns that rise more than 1,280 feet above the surrounding plains at Devils Tower National Monument, near the state's Black Hills region of the northeast. At Wyoming's Red Desert, south of Lander, the Continental Divide splits to form an enclosed basin where no water can escape, and nearby you find Fossil Butte National Monument, an archaeological treasure chest of fossilized fish and ancient miniature horses.

The states are characterized by long, cold winters and short summers of hot days and chilly nights. Temperature ranges are dramatic, and are largely dependent on elevation. Except along the far western edge of Montana, precipitation here is less than 30 inches a year. It's considerably less as you journey east and south. But the snowpack in the high mountains -- more than 300 inches accumulate in some areas -- melts through the summer and keeps the rivers running.

Planning a trip to Montana and Wyoming can be done in several ways. Those interested in a particular activity, such as hiking, might choose two or three locations and divide their time among them. Conversely, one could first select a destination, such as one of the national parks or an Old West town, and then determine the activities to be pursued there.

Yellowstone Plateau -- Yellowstone sits atop a volcanic caldera that periodically blows its top -- once every 600,000 years, give or take -- but in the interim provides a largely intact ecosystem in this park of 2.2 million acres. Protected from major development by the National Park Service, Yellowstone provides habitat no longer found elsewhere in the Lower 48, and is home to herds of bison, elk, grizzly bears, trumpeter swans, Yellowstone cutthroat trout, and more subtle beauties such as wildflowers and hummingbirds. The geothermal area is greater than any other in the world, with mud pots, geysers, and hot springs of all colors, size, and performance, indicative of a complex natural plumbing system that pulls water down into the earth's crust and regurgitates it at high temperatures. More than three million visitors come here annually, not just to pay homage to Old Faithful, but also to fish, hike, camp, and boat.

The Tetons & Jackson Hole -- The Tetons are a young range, abrupt and sharp edged as they knife up from the plain below. And while the photogenic peaks get top billing, it's the valley of Jackson Hole that provides the more varied environments and experiences. Grand Teton National Park offers some of the most stunning scenery most of us will ever see -- shimmering lakes, thickly carpeted forests, and towering peaks that are blanketed with snow throughout most of the year. It's an easy-to-see park -- you can catch its breathtaking beauty on a quick drive -- but you'll find lakes and waterfalls and even better views and adventures if you leave your car and take to the trails and waterways. The Tetons are especially popular with mountain climbers, who scale its peaks year-round. Elsewhere in the valley you can float the lively Snake River, visit the National Elk Refuge in the winter, or play cowboy at one of the dude and guest ranches that dot the valley. Skiers and snowboarders have a blast at the resorts here, as well as Grand Targhee on the other side of Teton Pass. And the snug town of Jackson, with its antler-arched town square and its busy shops, offers everything from classy art galleries to noisy two-steppin' cowboy bars.

North-Central Wyoming -- This is the sort of basin settlers were looking for when they came this way in the 19th century -- mountain ranges on all sides cradling wide, ranchable bottomlands, and some mineral wealth to pay for ranch kids' college educations. More and more, though, the oil and gas development, sheep herding and cattle driving, and beet and wheat growing are giving way to recreation and tourism. The beautiful mountains here -- the Wind Rivers, the Owl Creeks, the Absarokas, the east side of the Bighorns -- get less attention than the Tetons, but that only makes them more attractive. Historically, the area learned its lessons in tourism from the West's greatest showman, Buffalo Bill Cody, who helped build the fun-loving town that still bears his name. The rodeo and great museum of Cody are joined by other attractions, including the Bighorn Canyon National Recreation Area, the hot springs of Thermopolis, and the Wind River Indian Reservation, home to the Shoshone and Arapaho peoples.

Eastern Wyoming -- The plains don't begin when you pass east over the Continental Divide; there's another mountain range to cross, and then another -- first the Bighorns, then the Black Hills -- before you're really out there on the howling flats. The Bighorns are a treasure of steep canyons, snow-crowned peaks, good fishing, and good hiking, and at their feet sit two of Wyoming's nicest communities, Sheridan and Buffalo. Some of the prize ranches in this valley have become some of the best dude ranches in the country. Farther east, across the plains beyond the energy boomtown of Gillette, stands the unmistakable geological landmark that is Devils Tower, and along Wyoming's eastern border rise the Black Hills. The region's other claim to fame lies in its history. This is the land of Butch Cassidy and his Hole-in-the-Wall Gang (also known as the Wild Bunch), of cattle rustlers, cowboys, and outlaws.

Southern Wyoming -- To the millions of drivers who cross Wyoming on I-80, this is the empty quarter, consisting of mostly barren, wind-swept plains. But it also has its own mountainous corner -- the craggy Medicine Bow -- a lot of history, and mineral wealth of many varieties, from natural gas to trona. More discerning travelers will not see a wasteland: They'll follow the routes of Oregon Trail pioneers (you can still find the wagon-wheel ruts and graves), get off the freeway to visit historic sites such as Fort Laramie, and throw out a fishing line on the North Platte near Saratoga or in Flaming Gorge Reservoir south of Green River. In this country you'll find both old and new -- from the historic getaway of Saratoga to the capital city of Cheyenne, where the city throws the biggest rodeo party in the West during July's Cheyenne Frontier Days.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.