The Coast Range
The Coast
Range encompasses the entire western
portion of Lane County, extending from the Pacific Ocean to the
Willamette Valley and abutting the Western Cascades south of the
Valley. The general level of the crestline is 1,500 feet, though many
rounded ridges and peaks are higher. Near the ocean beaches, shifting
and stabilized sand dunes alternate with marine terraces and rugged
headlands. The interior is made up of many steep-sloped hills and
ridges increased by numerous stream canyons. The Siuslaw River flows
through the region, draining a large portion of the range.
The Southern Willamette Valley
The
Willamette Valley is the only sizable humid
lowland in Oregon, consisting of a broad plain. From an elevation
of nearly 430 feet at Eugene, the valley slopes gently northward to the
Columbia River. The slope is too gentle for good natural drainage.
Coupled with the accretion of river sediments, this low slope results
in several tributaries flowing parallel to the Willamette for many
miles before converging with the main channel. A number of small
volcanic hills, such as Skinner's Butte in Eugene, rise up to 300 feet
above the valley floor.
The Western Cascades
The Western
Cascades are a deeply dissected range of
volcanic rocks much older than the youthful High Cascades. Most of the
surface consists of steep ridges running east-west between the gorges
cut by the upper courses and tributaries of the McKenzie and Willamette
Rivers. The range rises abruptly above the Willamette Valley and the
ridges gain steadily in elevation towards the east, with several
mountains reaching nearly 6,000 feet.
The High Cascades
The High
Cascades form the backbone of Oregon and
constitute an imposing physical barrier. The bulk of the range consists
of a high lava plateau with numerous volcanic vents and cones towering
above it. The Three Sisters volcanoes, all extensively glaciated, reach
elevations over 10,000 feet. Lava flows and glacial processes have
produced many small lakes and a few large ones, most notably Waldo
Lake. The Willamette and McKenzie Passes both cross the Cascades in
Lane County, but only the Willamette Pass remains open all winter.
