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The 'Oregon Coast Range' is a mountain range running north-south in western Oregon that extends over 200 miles from the Columbia River on the border of Oregon and Washington south to the middle fork of the Coquille River in the United States. It is thirty to sixty miles wide and averages around 1,500 feet in elevation. The oldest portions of the range are over 60 million years old, with volcanics and a forearc basin as the primary mountain building processes responsible for the range. It is part of the larger Pacific Coast Range that extends over much of the western edge of North America. The range creates a rain shadow effect for the Willamette Valley that lies to the east of the mountains, creating a more stable climate and significantly less rain than the coastal region of the state.

Contents

Geology

Climate

Sections

North

Central

South

Peaks

Rivers

References

Geology

Volcanic activity approximately 66 million years ago in the Cretaceous period created offshore islands beginning in the southern portion of the current range.Orr, Elizabeth and William Orr, and Ewart Baldwin. Geology of Oregon. Kendall/Hunt Publishing, 1992, 4th edition. 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 hot basalt flow a 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.

Exposed pillow lava in the Northern 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 36 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.

Climate

A mild maritime climate prevails throughout the range with temperature and precipitation varying due to elevation and distance from the coastline. Relationships Between Landscape Structure and Breeding Birds in the Oregon Coast Range, , Kevin, McGarigal, Ecological Monographs,
Characteristic 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 (150 cm) in some parts to up to 120 inches (300 cm), with the higher amounts coming in the higher elevations. The average high temperature in January is 36.3° F (2.4° C), and the average high in July is 61.9° F (16.6° C) with temperatures also varying by elevation. The further inland and the more southerly portions have a more Mediterranean climate that is more similar to the climate of the Willamette Valley. The Coast Range creates a rain shadow effect by forcing moisture laden clouds to rise by expelling moisture.^[1] This shields the Willamette Valley and causes a more even climate with mild winters and less precipitation than the Oregon Coast.^[2]

Sections

Road through the Northern section showing the mix of deciduous and coniferous trees.

The Oregon Coast Range is divided into three separate sections: North, Central, and South. In the south is the oldest portion of the range with formation beginning in the Paleocene era with the Roseburg volcanics, while the newest section is the northernmost portion formed first with the Siletz River Volcanics. The Central and Northern sections contain more sedimentary rocks from the mud, silt, sand, and other volcanic debris than the lower Southern section. Also, the Oregon Coast Range is home to over 50 mammal species, over 100 species of birds, and nearly 30 reptile or amphibian species that spent significant portions of their life cycle in the mountains.Northwest Forest Plan: Wildlife Habitat Relationships for the Coast Guide

North

Main articles: Northern Oregon Coast Range

Located in the northwest portion of Oregon this section of the range has peaks as high as 3706 feet (1130 m) for Rogers Peak.^[3] Forests here are considered to be some of the most productive timber land in the world.Oregon State University: Northern Coast Range Adaptive Management Area; Chapter 2: Physical and Biological Environment Trees include primarily Sitka Spruce, Western Redcedar, Douglas-fir, and Western Hemlock.Tree Dictionary: From the Forest to the Sea: A Story of Fallen Trees Other plants include huckleberry, salmonberry, salal, vine maple, Oregon grape, bracken fern, and thimble-berry among others.Biotic Aspection in the Coast Range Mountains of Northwestern Oregon, Ecological Monographs, Vol. 28, No. 1. (Jan., 1958), pp. 21-54. James A. Macnab. The northern boundary is the Columbia River, with some mountainous features on the north side of the river, and continues south for approximately 100 miles to the Salmon River where Oregon Route 18 crosses the range from the Willamette Valley to the Oregon Coast with width roughly 35 miles.

Central

The Central portion west of Corvallis

Main articles: Central Oregon Coast Range

Located between the Salmon River and the Umpqua River on the north and south, the Central range is bounded by the Willamette Valley on the east and the Pacific Ocean to the west. This approximately 90 mile^[4] long mountain range contains mountains as high as 4,022 feet (1,226 m) for Marys Peak.USGS: GNIS Portions of the range are inside the Siuslaw National Forest along with three designated wilderness areas: Drift Creek Wilderness, Cummins Creek Wilderness and the Rock Creek Wilderness. Larger animals that live in these section include deer, elk, bobcat, and bear.Kerr, Andy. 1980. Last Stand for Oregon's Coast Range. Not Man Apart. Vol. 10, No. 1. January. 7. Bear are black bear while deer are mule and black-tailed deer species. Other mammals here are Mountain Beaver, beavers, coyote, mink, river otter, mountain lion, porcupines, skunks, and brush rabbit.

South

Main articles: Southern Oregon Coast Range

The southernmost section of the Coast Range is located in the southwest portion of Oregon between the middle fork of the Coquille River in the south and the Umpqua River on the north. Oregon Route 38 is the general divide between the Central and Southern portions of the Coast Range. Approximately 55 miles long, the section contains mountains as high as 3547 feet for Bone Mountain.USGS: GNIS On the south the Coquille River’s middle fork provides the general dividing line between the Central Range and the Klamath Mountains to the south and east.
Birds living in the Southern Coast Range include a variety of smaller and larger bird species. Species include peregrine falcons, pileated woodpeckers, olive-sided flycatcher, and western bluebirds among others.Fish and Wildlife Service: Notice of intent, to conduct scoping meetings The threatened Northern Spotted Owl also inhabit the mountain forests.SPOTTED OWL HOME RANGE AND HABITAT USE IN SOUTHERN OREGON COAST RANGES Animal life in the rivers, streams, and lakes include lamprey, coastal cutthroat trout, dace, Umpqua chub, frogs, salamander, turtles, coho salmon, steelhead trout, and others.

Peaks

Marys Peak

Five tallest peaks in the Oregon Coast Range:

★ Marys Peak, 4097 feet

★ Rogers Peak, 3661 feet

★ Grass Mountain, 3563 feet

★ Laurel Mountain, 3553 feet

★ Bone Mountain, 3547 feet

Rivers

Map of the region with major rivers in blue. Orange line shows divide between watersheds.

The following rivers have their headwaters in the Oregon Coast Range:

★ Drains to Pacific Ocean:

★
★ Alsea River

★
★ Coos River

★
★ Coquille River

★
★ D River

★
★ Kilchis River

★
★ Little Nestucca River

★
★ Miami River

★
★ Necanicum River

★
★ Nehalem River

★
★ Nestucca River

★
★ Salmonberry River

★
★ Salmon River

★
★ Siletz River

★
★ Siltcoos River

★
★ Siuslaw River

★
★ Smith River

★
★ Tillamook River

★
★ Trask River

★
★ Umpqua River

★
★ Wilson River

★
★ Yachats River

★
★ Yaquina River

Nestucca River in the Northern range.

★ Drains to Columbia River:

★
★ Clatskanie River

★
★ John Day River

★
★ Klaskanine River

★
★ Lewis and Clark River

★
★ Skipanon River

★
★ Wallooskee River

★
★ Youngs River

★ Drains to Willamette River:

★
★ Coast Fork Willamette River

★
★ Long Tom River

★
★ Luckiamute River

★
★ Marys River

★
★ Tualatin River

★
★ Yamhill River

References

1. Encyclopedia Britannica: orographic precipitation
2. Encyclopedia Britannica: Oregon climate
3. Peakbagger.com: Rogers Peak
4. Peakbagger.com: Central Oregon Coast Range