Washington has seven geographic regions. In the northwest, the Olympic Peninsula includes the rugged Olympic Mountains, which are covered in rainforest. The Willapa Hills run north-south from Grays Harbor to the Columbia River in the southwest and are covered in forested slopes. To the north and east of the Willapa Hills are the fertile Chehalis and Cowlitz valleys.
The Puget Sound Lowland region stretches southward from Canada between the Olympic Mountains and the Cascade Range to join the valleys of the Chehalis and Cowlitz rivers, which form an extension to the Columbia River. This area includes Puget Sound itself. The Cascade Mountain Range is east of the Puget Sound Lowland and has the state’s highest mountains. Its volcanic peaks includes 14,410-foot (4,392-metre) Mount Rainier, the fifth highest peak in the mainland United States. Mount St. Helens is also in the Cascades, near the Oregon border. It erupted violently in 1980 and blasted away its volcanic cone, reducing the mountain’s height from 9,677 feet (2,950 metres) to 8,363 feet (2,549 metres). The highest peaks of the Cascades have permanent glaciers.
The Columbia basin region is in central Washington. It is a plateau and its largest rivers are the Columbia and Snake rivers. The Okanogan Highlands are in the northeast, and the Blue Mountains are in the southeastern corner of the state.
The Cascade Mountains contain a number of still-active volcanoes. Most of these were dormant during the second half of the 19th century and most of the 20th. Early in 1980, however, Mt. St. Helen’s began to show ominous signs of activity. On 18 May, the volcano exploded, blasting more than 1,300 ft (400 m) off the top of the mountain. Tremendous plumes of steam and ash were thrust into the stratosphere, where winds carried volcanic dust thousands of miles eastward. The areas surrounding Mt. St. Helen's were covered in ash and mudflows several feet deep in place, choking local streams and lakes, and nearby towns. The eruption also left 57 people dead or missing. Another minor eruption, on 14 May 1984, shot ash 4 mi (6 km) high and caused a small mudflow down the mountain's flanks, but no injuries or other damage occurred. Today, animals driven away from the slopes of Mt. St. Helen's by the eruption have returned. On 17 August 1982, the Mt. St. Helen's National Volcanic Monument was created by Congress; it includes about 110,000 acres (44,500 ha) of the area that had been devastated by the eruption.
Washington has a large number of rivers. The longest and most powerful is the Columbia, which entering the northeastern corner of Washington from Canada and flows for more than 1,200 mi (1,900 km) across the state, and then along the Oregon border to the Pacific Ocean. Washington's other major river, the Snake, enters the state from Idaho in the southeast and flows westward, joining up with the Columbia River near Pasco.
Washington also has many lakes. The largest is the artificial Franklin D. Roosevelt Lake, covering 123 sq mi (319 sq km). Washington has some 90 dams, providing water storage, flood control, and hydroelectric power. One of the largest and most famous dams in the US is Grand Coulee on the upper Columbia River, which is 550 ft (168 m) high and 4,173 ft (1,272 m) long.
The climate in Washington can vary depending on which side of the Cascade Mountains you are on. To the west of the Cascade Mountains, the warm ocean waters give a milder climate that would other be expected this far north. Average January temperatures Seattle are in the low 40s F (about 5 °C) and average July temperatures are in the mid-60s F (about 19 °C). Rainfall here is often more than 200 inches (5,000 mm) a year. To the east of the Cascades, the weather is more variable. In the summer, there are usually a few days of temperatures over 100 °F (38 °C). In the winter, the Rocky Mountains shield the region from cold Canadian air, but average January temperatures are still in the mid-20s F (about −4 °C). Annual rainfall is also much lower than in the west, from around 17 inches (430 mm) in Spokane to less than 8 inches (200 mm) in the lower Yakima valley.
The lowest temperature ever recorded in the state is –48°F (–44°C), set at Mazama and Winthrop on 30 December 1968; the highest, at Ice Harbor Dam on 5 August 1961, was 118°F (48°C). Paradise Ranger Station holds the North American record for the most snowfall in one season, when 1,122 in (2,850 cm) of snow fell during the winter of 1971–72. High mountain peaks, such as Mt. Adams, Mt. Baker, and Mt. Rainier, have permanent snowcaps or snowfields of up to 100 ft (30 m) deep.
