Map of the Cascade Range showing major volcanic peaks
The Cascades extend northward from
Lassen Peak (also known as Mount Lassen) in northern
California to the confluence of the
Thompson rivers in
British Columbia. The
Fraser River separates the Cascades from the
Coast Mountains. The highest volcanoes of the Cascades, known as the High Cascades, 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 or more. The highest peaks, such as the 14,411-foot (4,392 m) Mount Rainier, dominate their surroundings for 50 to 100 miles (80 to 161 km).
The northern part of the range, north of Mount Rainier, is known as the
North Cascades in the United States but is formally named the Cascade Mountains north of the
Canada–United States border, reaching to the northern extremity of the Cascades at
Lytton Mountain. Overall, the North Cascades and Canadian Cascades are extremely rugged; even the lesser peaks are steep and glaciated, and valleys are quite low relative to peaks and ridges, so there is great local
relief. The southern part of the Canadian Cascades, particularly the
Skagit Range, is geologically and topographically similar to the North Cascades, while the northern and northeastern parts are less glaciated and more plateau-like, resembling nearby areas of the
Because of the range's proximity to the Pacific Ocean and the region's
prevailing westerly winds, precipitation is substantial, especially on the western slopes due to
orographic lift, with annual snow accumulations of up to 1,000 inches (25,000 mm) in some areas.
Mount Baker in Washington recorded a world-record single-season snowfall in the winter of 1998–99 with 1,140 inches (29,000 mm).
 Prior to that year,
Mount Rainier held the world record for snow accumulation at Paradise in 1978. It is not uncommon for some places in the Cascades to have over 500 inches (13,000 mm) of annual snow accumulation, such as at
Lake Helen, near Lassen Peak.
 Most of the High Cascades are therefore white with snow and ice year-round. The western slopes are densely covered with
Douglas-fir (Pseudotsuga menziesii),
western hemlock (Tsuga heterophylla) and
red alder (Alnus rubra), while the drier eastern slopes feature mostly
ponderosa pine (Pinus ponderosa), with some
western larch (Larix occidentalis),
mountain hemlock (Tsuga mertensiana) and
subalpine fir (Abies lasiocarpa) and
subalpine larch (Larix lyallii) at higher elevations. Annual rainfall is as low as 9 inches (230 mm) on the eastern
due to a
rain shadow effect.
Beyond the eastern foothills is an
arid plateau that was largely created 17 to 14 million years ago by the many flows of the
Columbia River Basalt Group. Together, these sequences of fluid
volcanic rock form the 200,000-square-mile (520,000 km2)
Columbia Plateau in eastern Washington, Oregon, and parts of western Idaho.
Columbia River Gorge is the only major break of the range in the United States. When the Cascades began to rise 7 million years ago in the
Pliocene, the Columbia River drained the relatively low Columbia Plateau. As the range grew, erosion from the Columbia River was able to keep pace, creating the gorge and major pass seen today. The gorge also exposes uplifted and warped layers of basalt from the plateau.