Montana, smaller only to Alaska, Texas and California, is the fourth largest state in the U.S. The name Montana orginates from a Spanish word meaning mountainous. Early travelers who saw the sun glistening on the lofty, snow-capped peaks called the area The Land of Shining Mountains. The central and western thirds of the state have numerous mountain ranges (approximately 77 named) of the northern Rocky Mountains; thus the state's name, derived from the Spanish word montaña ("mountain"). The state nickname is the "Treasure State." Other nicknames include "Land of Shining Mountains," "Big Sky Country," and the slogan "the last best place." The state ranks fourth in size but has a relatively low population (with only six states having fewer people) and consequently a very low population density. The economy is primarily based on agriculture and significant lumber and mineral extraction. [citation needed] Tourism is also important to the economy, with millions of visitors a year to Glacier National Park, the Battle of Little Bighorn site, and three of the five entrances to Yellowstone National Park. the state of Montana is the fourth largest in the United States (after Alaska, Texas, and California). To the north, Montana and Canada share a 545-mile (877 km) portion of the world's longest undefended border. The state borders the Canadian provinces of British Columbia, Alberta, and Saskatchewan, more provinces than any other state. To the east, the state borders North Dakota and part of South Dakota. To the south is Wyoming and about a mile of South Dakota, and on the west and southwest is Idaho. The topography of the state is diverse, but roughly defined by the Continental Divide, which runs on an approximate diagonal through the state from northwest to south-central, splitting it into two distinct eastern and western regions. Montana is well known for its mountainous western region, part of the northern Rocky Mountains. However, about 60% of the state is actually prairie, part of the northern Great Plains. Nonetheless, even east of the Continental Divide and the Rocky Mountain Front, there are a number of isolated "Island Ranges" that dot the prairie landscape. St. Mary's Lake in Glacier National ParkThe Bitterroot Mountains divide the state from Idaho to the west with the southern third of the range blending into the Continental Divide. Mountain ranges between the Bitterroots and the top of the Continental Divide include the Cabinet Mountains, the Missions, the Garnet, Sapphire, Flint Creek, and Pintlar ranges. The northern section of the Divide, where the mountains give way rapidly to prairie, is known collectively as the Rocky Mountain Front and is most pronounced in the Lewis Range located primarily in Glacier National Park. Due to the configuration of mountain ranges in Glacier National Park, the Northern Divide (which begins in Alaska's Seward Peninsula) crosses this region and turns east in Montana at Triple Divide Peak. Thus, the Waterton, Belly, and Saint Mary rivers flow north into Alberta, Canada, joining the Saskatchewan River and ultimately emptying into Hudson Bay. East of the Divide, several parallel ranges march across the southern half of the state, including the Gravelly Range, the Tobacco Roots, the Madison Range, Gallatin Range, Big Belt Mountains, Bridger Mountains, Absaroka Mountains, and the Beartooth Mountains. The Beartooth Plateau is the largest continuous land mass over 10,000 feet (3,000 m) in the lower 48 states and contains the highest point in the state, Granite Peak, 12,799 feet (3,901 m) high. Between the mountain ranges are many scenic valleys, rich in agricultural resources and rivers, and possessing multiple opportunities for tourism and recreation. Among the best-known areas are the Flathead Valley, Bitterroot Valley, Big Hole Valley, and Gallatin Valley. Pompeys Pillar National MonumentEast and north of this transition zone are expansive sparsely populated Northern Plains, with rolling tableland prairies, "island" mountain ranges, and scenic badlands extending into the Dakotas, Alberta, Saskatchewan, and Wyoming. The isolated island ranges east of the Divide include the Castle Mountains, Crazy Mountains, Little Belt Mountains, Snowy Mountains, Sweet Grass Hills, Bull Mountains and, in the southeastern corner of the state near Ekalaka, the Long Pines and Short Pines. The area east of the divide in the north-central portion of the state is known for the dramatic Missouri Breaks and other significant rock formations. Three stately buttes south of Great Falls are familiar landmarks. These buttes, Square Butte, Shaw Butte, and Crown Butte, are made of igneous rock, which is dense and has withstood weathering for many years. The underlying surface consists of shale. Many areas around these buttes are covered with clay surface soils. These soils have been derived from the weathering of the Colorado Formation. Farther east, areas such as Makoshika State Park near Glendive, and Medicine Rocks State Park near Ekalaka also highlight some of the most scenic badlands regions in the state. Montana also contains a number of rivers, many of which are known for "blue-ribbon" trout fishing, but which also provide most of the water needed by residents of the state, as well as being a source of hydropower. Montana is the only state in the union whose rivers form parts of three major North American watersheds: The Pacific Ocean, the Gulf of Mexico, and Hudson Bay which are divided atop Triple Divide Peak in Glacier National Park. West of the divide, the Clark Fork of the Columbia (not to be confused with the Clarks Fork of the Yellowstone River) rises in the Rocky Mountains near Butte, flows west toward Missoula where it is joined by the Blackfoot River and the Bitterroot River, and turns to the northwest, entering Idaho just above Lake Pend Oreille, becoming part of the Columbia River, which flows to the Pacific Ocean. The Clark Fork discharges the greatest volume of water of any river exiting the state. The Flathead River and Kootenai River also drain major portions of the western half of the state. East of the divide, the Missouri River, formed by the confluence of the Jefferson, Madison, and Gallatin rivers, crosses the central part of the state, flows through the Missouri breaks and enters North Dakota. The Yellowstone River rises in Yellowstone Park in Wyoming, flows north to Livingston, Montana, where it then turns east and flows across the state until it joins the Missouri River a few miles east of the North Dakota boundary. The Yellowstone River is the longest undammed, free-flowing river in North America. Other major Montana tributaries of the Missouri include the Milk, Marias, Tongue, and Musselshell Rivers. Montana also claims the disputed title of possessing the "world's shortest river," the Roe River, just outside Great Falls, Montana. These rivers ultimately join the Mississippi River and flow into the Gulf of Mexico. Water is of critical importance to the state for both agriculture and hydropower. In addition to its rivers, the state is home to Flathead Lake, the largest natural fresh-water lake west of the Great Lakes. Man-made reservoirs dot Montana's rivers, the largest of which is Fort Peck Reservoir, on the Missouri river, contained by the largest earth-filled dam in the world. Vegetation of the state includes ponderosa pine, lodgepole pine, larch, fir, spruce, aspen, birch, red cedar, ash, alder, rocky mountain maple and cottonwood trees. Forests cover approximately 25% of the state. Flowers native to Montana include asters, bitterroots, daisies, lupins, poppies, primroses, columbine, lilies, orchids and dryads. Several species of sagebrush and cactus and many species of grasses are common. Many species of mushrooms and lichens are also found in the state. Montana contains Glacier National Park and portions of Yellowstone National Park, including three of the Park's five entrances. Other federally recognized sites include the Little Bighorn National Monument, Bighorn Canyon National Recreation Area, Big Hole National Battlefield, Lewis and Clark Caverns, and the National Bison Range. Montana has eight National Forests and over 20 National Wildlife Refuges. The Federal government administers 36,000,000 acres. 275,000 acres are administered as state parks and forests. Areas managed by the National Park Service include: Big Hole National Battlefield near Wisdom Bighorn Canyon National Recreation Area near Fort Smith Glacier National Park Grant-Kohrs Ranch National Historic Site at Deer Lodge, Montana Lewis & Clark National Historic Trail Little Bighorn Battlefield National Monument near Crow Agency Nez Perce National Historical Park Yellowstone National Park Several Indian reservations are located in Montana: Fort Peck Indian Reservation, Fort Belknap Indian Reservation, Northern Cheyenne Indian Reservation, Crow Indian Reservation, Rocky Boy's Indian Reservation, Blackfeet Indian Reservation, and the Flathead Indian Reservation