Wyoming is made up of six main geographic areas. The eastern third of Wyoming is part of the Great Plains; the remainder belongs to the Rocky Mountains. However, the Rocky Mountains are divided into three separate ranges, called the Northern, Southern, and Middle Rocky Mountains. The Southern Rockies start in Colorado and include the Laramie mountains. The Northern Rocky Mountains start in Canada. In Wyoming, they include the northwestern corner of Yellowstone Park. The larger Middle Rocky Mountain region takes up most of the northwestern quarter of Wyoming, and includes the Bighorn and Wind River mountains, much of of Yellowstone Park, and Gannett Peak, the highest point in the state (13,804 ft/4,210 meters). The other two geographic regions in Wyoming are the Black Hills, and the Wyoming Basin, which borders the Continental Divide between the Southern and Middle Rocky Mountains and is made up of smaller mountains, with valleys between them. an area of lower land between the Plains and the mountains.The lowest point in the state—3,099 ft (945 m)—occurs in the northeast, on the Belle Fourche River.
Most of Wyoming's main rivers begin in the state and flow out to neighboring states. These rivers include the Green River, which flows into Utah; the Yellowstone, Big Horn, and Powder rivers, which flow into Montana; the Snake River, which flows into Idaho; the Belle Fourche and Cheyenne rivers, which flow into South Dakota; and the Niobrara and Bear rivers, which flow into Nebraska. The North Platte River enters Wyoming from Colorado and eventually flows out into Nebraska. These rivers all eventually flow into the Colorado, Columbia, and Missouri rivers and the Great Salt Lake. So, Wyoming waters flow into most of the major river systems of the west. These waters, which are so important to life the west, mostly begin as snow in Wyoming's mountain ranges. Wyoming's largest lake is Lake Yellowstone, which is in Yellowstone National Park. Two smaller lakes, Jackson and Jenny, are located in Grand Teton National Park.
Most of Wyoming is located at a high elevation, and has a dry near-desert climate. There are also areas of semiarid steppe (short-grass prairie), and alpine climates. The arid desert regions are all found in the western half of the state. In these areas, the average rainfall is only about 4 to 8 inches (100 and 200 mm) a year. Rainfall in the areas with a semiarid steppe climate averages around 9 to 16 inches (230 to 410 mm) a year. However, Wyoming’s mountains receive large amounts of precipitation in the form of snow. In some mountain areas more than 200 inches (5,100 mm) of snow falls each year, and can remain on the ground for more than 150 days per year. January mean temperatures range from a low of about 10 °F (–12 °C) in the mountains to the upper 20s F (about –2 °C) in the southeast. Mean July temperatures range from the low 50s °F (about 10 °C) in the mountains to the mid-70s F (about 24 °C) in the Bighorn Basin in north-central Wyoming. The record low temperature was -66°F (–54°C), set 9 February 1933 at Riverside; the record high was 114°F (46°C), set on 12 July 1900 at Basin.
