General · EdgepediaOctober 20, 20266 min read

Pacific Coast Ranges

The Pacific Coast Ranges, also referred to as the Coast Ranges or the Pacific Mountain System, are a system of mountain ranges along the Pacific coast of North America. Under a commonly used broad geographic definition the system runs about 3,800 miles (6,100 km) from Alaska through western Canada and the western United States into Mexico.¹ Rather than forming one continuous ridge, it consists of numerous individual mountain systems separated by valleys, lowlands, fjords, river corridors, and coastal plains.¹ Its highest summit is Mount Logan in the Saint Elias Mountains, at 19,551 feet (5,959 m).¹

Key fact	Detail
Extent	Alaska south through western Canada, the western United States, and into northern and central Mexico; about 3,800 miles (6,100 km) under a broad definition¹
Highest point	Mount Logan, Saint Elias Mountains, 19,551 feet (5,959 m), the highest mountain in Canada and the second-highest summit in North America¹
Tectonic setting	Coastal ranges of the Cascadia Subduction Zone form as an accretionary wedge, material scraped off the subducting Juan de Fuca Plate²
Typical elevation	Coast Ranges average about 3,300 feet (1,000 m), with some peaks and ridges above 6,600 feet (2,000 m)³
Structure	Not one continuous ridge but numerous individual systems separated by valleys, lowlands, fjords, river corridors, and coastal plains¹

Extent and definitions

Definitions are not identical among geographers and geological agencies: the terms Pacific Coast Ranges, Coast Ranges, Pacific Mountain System, and Pacific Border Province refer to overlapping but different groups of mountains, and some U.S. physiographic classifications place the Sierra Nevada within a wider Pacific Mountain System while the broad definition of the Pacific Coast Ranges treats it separately.¹

In the United States, the Pacific Border Province of the Pacific Mountain System includes the Olympic Mountains, the Oregon Coast Range, the Klamath Mountains, the California Coast Ranges, and the Los Angeles Ranges, together with lowlands such as the Puget Trough and the California Trough.⁴ The province is described as a geologically active area of rough mountains with elevations from sea level to more than 11,483 feet, where earth flows and complex landslides are active in mountainous areas.⁵

Component ranges

Rather than forming one continuous ridge, the system consists of numerous individual mountain systems separated by valleys, lowlands, fjords, river corridors, and coastal plains.¹

Northern ranges. The Pacific Ranges subdivision of the Coast Mountains contains its highest peaks, with a width of 80 to 100 miles between the Coastal Trough on the west and the Interior System on the east.⁶ The highest summit associated with the whole system is Mount Logan in the Saint Elias Mountains, at 19,551 feet (5,959 m).¹

United States ranges. The Olympic Mountains are the most rugged of the coastal ranges, with an average elevation of 1,500 m (5,000 ft), glacier-deepened valleys, and a tallest peak, Mount Olympus, at 2.4 km (7,965 ft); their rocks are Cenozoic sandstones, shales, conglomerates, and basalts metamorphosed to slates, phyllites, and greenstone.⁷ The Oregon Coast Ranges are made of Tertiary sandstones, shales, and limestones intruded by igneous bodies, while the California Coast Ranges consist of Cretaceous sedimentary and metamorphic rocks with Mesozoic granitic intrusions, deformed by ongoing faulting including the San Andreas Fault zone.⁷ The Klamath Mountains, higher and more rugged than either, are hard metamorphic Paleozoic rocks with Mesozoic sedimentary beds and volcanics, and they connect the Pacific Border ranges with the Sierra Nevada.⁷ Running south-southeast along the Pacific shoreline, the California Coast Ranges stretch 925 km (575 miles), beginning at Cape Mendocino, continuing beyond San Francisco Bay, and ending at Point Conception; the Great Valley lies between them and the Sierra Nevada.⁸ All ranges of the province trend north-south except the Transverse Ranges, which trend east-west and are the most variable in rock type and elevation, rising from 900 m (3,000 ft) to more than 3,000 m (10,000 ft).⁷

Tectonic origin

The coastal ranges owe their existence to subduction, the sinking of dense oceanic crust beneath the North American plate. Where plates converge this way, two parallel mountain belts commonly develop: a coastal range of sedimentary strata and hard rock lifted out of the sea, called an accretionary wedge, and a volcanic arc farther inland.² In the Pacific Northwest, the Coast Range, Olympic Mountains included, is built from sedimentary strata plus stiff oceanic crust scraped from the seabed at the point where subduction of the Juan de Fuca Plate begins, whereas the Cascade Range rises farther east over the plate's deeper descent; between the two ranges lies the lowland made up of Puget Sound, the Willamette Valley, and the Great Valley.²

The rocks record long-distance travel as well as scraping. The Coast Range ophiolite of California, a slab of oceanic lithosphere, formed 169 to 163 million years ago in a forearc or back-arc setting at equatorial latitudes and was accreted to the California margin of North America at about 145 million years ago, during the Late Jurassic, after rapid northward translation on a fast-moving plate of the eastern Pacific basin.⁹ Farther north, the basement of the Oregon Coast Range was formed by a volcanic island chain that collided with North America about 50 million years ago; its ancient volcanoes form many of the scenic headlands along the coast.¹⁰ Because the subducting oceanic crust moves oblique to the north-trending edge of the continent, the rocks of the Coast Ranges are also being shuffled northward and rotating slowly clockwise.¹¹

Regional character

Elevation and climate vary along the length of the system. The Coast Ranges of the United States average about 3,300 feet (1,000 m) above sea level, with some peaks and ridges rising above 6,600 feet (2,000 m), and have cool summers and mild winters in the north with drier summers in the south.³ In Oregon, the Coast Range ecoregion runs from sea level to Marys Peak at roughly 4,100 feet, with main ridge summits around 1,400 to 2,500 feet; its maritime climate of warm, dry summers and mild, very wet winters supports highly productive temperate rainforests dominated by conifers.¹² Storms arriving from the Pacific drop most of their moisture on the Coast Range and Cascades, leaving eastern Oregon and Washington dry, a pattern that shapes plant and animal communities as well as human land use.²

The mountains remain geologically active. Individual earthquakes offset or lift the land a few centimeters at a time, and over millions of years such movements build coastal ranges even as wind, rain, and waves wear the landscape back down.² The steep, actively deforming terrain makes parts of the system slide-prone; the Coast Ranges of California are among the regions of the United States with high landslide incidence.¹³

References

Topic: Encyclopedia › Places and geography › Landforms and terrestrial features › Mountains, plains, and other land terrain › Mountain ranges, ridges, and hill systems › North American ranges

Initially written Oct 20, 2026 · Edited: Oct 25, 2026

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