Oregon Coast Range

The Oregon Coast Range, often called simply the Coast Range and sometimes the Pacific Coast Range, is a mountain range, in the Pacific Coast Ranges physiographic region, in the U.S. state of Oregon along the Pacific Ocean. This north-south running range extends over 200 miles (320 km) from the Columbia River in the north on the border of Oregon and Washington, south to the middle fork of the Coquille River. It is 30 to 60 mi (48 to 97 km) wide and averages around 1,500 feet (460 m) in elevation above sea level. The coast range has three main sections: the Northern, Central, and Southern Ranges.

The oldest portions of the range are over 60 million years old, with volcanic activity and a forearc basin being the primary mountain building processes responsible for the mountains. It is part of a larger grouping known as the Pacific Coast Ranges that extends over much of the western edge of North America from California to Alaska. The range creates a rain shadow effect for the Willamette Valley, which lies to the east of the Coast Range and west of the Cascade Range. This rain shadow creates a stable climate in the valley, with significantly less rain than the Oregon Coast. On the western side of the range, the same rain shadow causes more precipitation to fall, contributing to the numerous rivers that flow into the Pacific Ocean.

Marys Peak in the Central Coast Range is the highest peak at 4,097 ft (1,248 m). Both the state and federal government manage forests throughout the Oregon Coast Range, where logging is a major industry in both private and government owned forests. The mountains are home to a variety of wildlife including black bear, elk, deer, beaver, and many species of birds. Fish including salmon and trout, in addition to many other aquatic organisms inhabit the range's streams and rivers.

Volcanic activity approximately 66 million years ago in the Cretaceous Period created offshore islands beginning in the southern portion of the current range. These Roseburg volcanics were followed by the Siletz River Volcanics in the northern portions of the range, and lastly a series of basalt flows from the Columbia River basalts also added to these formations with some smaller flows in-between. Much of the formations are the result of pillow basalt formations created when a hot basalt flow rapidly cooled upon meeting the salt water of the ocean. These deposits offshore were then pushed into the continental plate as a forearc basin rotating slowly over millions of years. This tectonic collision forced the basalt formations (and newer sedimentary rock formations that include marine terrace deposits) upward and created the coastal range.

Additional basalt flows originated from Eastern Oregon and added to the layers that were uplifted, as the newer Cascade Mountains had not yet been formed. By the Early Oligocene period c. 30 million years ago the current coastline was in place and erosion has continued to shape the range. primarily through rivers cutting deep valleys through the igneous and sedimentary rocks.

The geologic boundaries of the coast range formation extend from southwest Washington state in the north to around the Coquille River in the south where the older and taller Klamath Mountains begin. In the east the mountains begin as foothills forming the western edge of the Willamette Valley and continue west to the coastline and beyond where the basalt formation tapers off into the continental shelf and ends at the continental slope with several banks and basins off shore.

Physiographically, they are a section of the larger Pacific Border province, which in turn are part of the larger Pacific Mountain System physiographic division.

A mild maritime climate prevails throughout the range with temperature and precipitation varying due to elevation and distance from the coastline. Characteristics of the climate include cool dry summers followed by mild and wet winters. The majority of precipitation accumulates in the form of rain, with snow during the winter months at the higher elevations, but no permanent snow pack. Annual precipitation differs from 60 inches (1,500 mm) in some parts to up to 120 in (3,000 mm), with the higher amounts coming in the higher elevations.