The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades. The small part of the range in British Columbia is called the Canadian Cascades or Cascade Mountains; the latter term is also sometimes used by Washington residents to refer to the Washington section of the Cascades in addition to North Cascades, the more usual American term, as in North Cascades National Park.

The Cascades are part of the Pacific Ring of Fire, the ring of volcanoes and associated mountains around the Pacific Ocean. All of the known historic eruptions in the contiguous United States have been from Cascade volcanoes. The two most recent were Lassen Peak in 1914 to 1921 and a major eruption of Mount St. Helens in 1980. Minor eruptions of Mount St. Helens have also occurred, most recently in 2006.

Geography

At its southern end the range is about 30 to 50 miles (50 to 80 km) wide and 4,500 to 5,000 feet (1,370 to 1,520 m) high and 80 miles (130 km) wide in northern Washington. At its northern apex at Lytton Mountain (2,049 m) in Canada, near the confluence of the Fraser and Thompson Rivers, the range is only wide. The tallest volcanoes of the Cascades are called the High Cascades and dominate their surroundings, often standing twice the height of the nearby mountains. They often have a visual height (height above nearby crestlines) of one mile (1.6 km) or more. The tallest peaks, such as the 14,411 foot (4,392 m) high Mount Rainier, dominate their surroundings for 50 to 100 miles (80 to 160 km).

The northern part of the range, north of Mount Rainier, is known as the North Cascades. It is extremely rugged, with many of the lesser peaks steep and glaciated. The valleys are quite low, resulting in great local relief, and major passes are only about 1,000 m (3,300 ft) high. The southern part of the Canadian Cascades are included in the North Cascades, and have the same geography and geology. Usage differs as to whether to include the Coquihalla Range, which reaches up to the confluence of the Fraser and Thompson Rivers. Its northern reaches have very different terrain and geology, more resembling the plateau country which extends north and east from the range's terminus at Lytton Mountain.

Beyond the foothills is an arid plateau that was created 16 million years ago as a coalescing series of layered flood basalt flows. Together, these sequences of fluid volcanic rock form a 200,000 square mile (520,000 km²) region out of eastern Washington, Oregon, and parts of Northern California and Idaho called the Columbia River Plateau.