Central Oregon Coast Range

Central Oregon Coast Range
The range from west of Corvallis
Highest point
Peak	Marys Peak
Elevation	4,097 ft (1,249 m)
Coordinates	44°30′16″N 123°33′09″W / 44.50435595°N 123.552456264°W / 44.50435595; -123.552456264
Dimensions
Length	90 mi (140 km) North–South
Geography
Country	United States
State	Oregon
Range coordinates	44°36′00″N 123°34′00″W / 44.6°N 123.566667°W / 44.6; -123.566667Coordinates: 44°36′00″N 123°34′00″W / 44.6°N 123.566667°W / 44.6; -123.566667
Parent range	Oregon Coast Range
Borders on	Northern Oregon Coast Range and Southern Oregon Coast Range
Geology
Age of rock	Paleocene and Eocene
Type of rock	volcanic and forearc basin

The Central Oregon Coast Range is the middle section of the Oregon Coast Range, in the Pacific Coast Ranges physiographic region, and located in the west-central portion of the state of Oregon, United States roughly between the Salmon River and the Umpqua River and the Willamette Valley and the Pacific Ocean. This approximately 90-mile (140 km) long mountain range contains mountains as high as 4,097 feet (1,226 m) for Marys Peak. Portions of the range are inside the Siuslaw National Forest and three wilderness areas exist as well: Drift Creek Wilderness, Cummins Creek Wilderness and Rock Creek Wilderness.

The underlying rock of the Central Coast Range are the igneous rocks from the Siletz River Volcanics of the Paleocene age. It is estimated that this rock formation is up to 16 miles (26 km) thick. These formations consist mainly of pillow basalt, large lava flows, tuff-breccia, and sills. This part of the mountains are approximately 50 to 60 million years old. It is theorized that the source of these lava flows came from oceanic islands that formed over a tectonic hotspot. The entire Oregon Coast Range overlies a convergent tectonic margin that interacts with the Juan de Fuca Plate that is being sub-ducted beneath the North America tectonic plate. This is the Cascadia subduction zone that has experienced uplift for several million years. Currently it is part of a large forearc basin that extends for much of the entire Coast Range on a north-south alignment. Parts of the upper portions of the range contain continental margin deposits from the early Eocene to Paleocene age. Portions of this include marine fossils in the geologic record. Sandstone and shale are also present in the sections of the mountains, with thickness up to 7,875 ft (2,400 m). In the southern part of the range the bedrock is overlaid by Eocene age turbidite sediments and river sediment. The active tectonic forces have created many faults and folds in the range. Additionally, erosion is a major landscape-shaping force for the range. Both heavy rainfall and the resulting landslides have worked to erode and shape the mountains. Much of the landscape is dominated by steep slopes and drainages that are deeply cut into the hillsides from the erosion. Unlike many areas in North America, the mountain range did not see glaciations during the age.