Willamette and Coast Demarcation
Starting just west of Rainier on the bank of Columbia River in Columbia County, the line of demarcation between Willamette and Coast provinces in Oregon goes west atop steep slopes overlooking Columbia River at about 500 feet elevation. About 6 miles east of Clatskanie, the line veers sharply to the south on topography about 750 to 1,000 feet elevation that is west of Clatskanie River. At the ridge that separates the Clatskanie and Nehalem river drainages, the line turns northwest along the north side of Nehalem River drainage at about 1,000 feet elevation. In the upper reaches of Fishhawk Creek, the line travels south to cross Nehalem valley less than a mile west of Nehalem community at about 600 feet elevation. From there, it ascends the ridge leading south to Green Mountain where, at an elevation of about 1,750 feet, it circles east and south of the mountain and crosses Sunset Highway (U.S. 26) in the headwaters of Rock Creek at about 1,600 feet elevation.
From the summit pass on Highway 26, the line winds southeast at about 1,750 feet elevation to the Tillamook–Washington county line. It turns south at that elevation around the east and south sides of Round Top and the headwaters of Gales Creek. It crosses the pass between Gales Creek and Wilson River at about 1,600 feet elevation and returns to 1,750 feet elevation to run south around the headwaters of drainages flowing eastward into Tualatin and North Yamhill rivers.
Northwest of McMinnville, the line makes a huge swing westward at about 1,750 feet elevation around the headwaters of drainages flowing south into South Yamhill River. The line crosses Highway 22 northwest of Grande Ronde at about 670 feet elevation and crosses Highway 18 in Van Duzer State Park at about 770 feet elevation. This is the pass between the Yamhill and Salmon river drainages.
From Van Duzer State Park, the line ascends the ridge to the south. Within about 3 miles it is again at about 1,750 feet elevation on Saddleback Mountain. From there, it goes east and south at about 1,750 feet elevation around headwaters of drainages flowing into Yamhill and Little Luckiamute rivers. From the south side of Monmouth Peak in southwest Polk County, the line descends the ridge southeasterly to cross Luckiamute River at about 650 feet elevation. It climbs Cougar Ridge and then winds south along the crest of the Coast Range. The Coast Range drops in elevation on the narrow divide between Marys River and Yaquina River to about 730 feet elevation at the community of Summit, about 5 miles northwest of Blodgett on Highway 20.
From the community of Summit, the line continues west and south along the crest of the Coast Range to cross the Corvallis–Newport Highway (U.S. 20) at about 800 feet elevation about 2 miles northwest of Burnt Woods community. This is the pass between Tumtum River flowing east and Little Elk Creek flowing west. From there, the line goes south along the crest of the Coast Range to Marys Peak, winding north and east around Mary’s Peak at about 1,700 feet elevation. The line crosses the pass on Alsea Highway (Oregon 34) at about 1,125 feet elevation, runs southeast up the ridge and around the east slopes of Flat Mountain at about 1,750 feet elevation, and continues south at about that elevation. This is the crest of the Coast Range between drainages flowing into Alsea River to the west and Long Tom River to the east.
The line of demarcation between Willamette and Coast provinces continues south along the crest of the Coast Range to the pass between Wildcat Creek to the west and Noti Creek to the east, which is about 6 miles southwest of Fern Ridge Reservoir. The line continues to wind southeasterly along the crest of the Coast Range, then descends into the Siuslaw River drainage to cross the river about 12 miles downriver from Lorane community, which is northwest of Cottage Grove. From the river crossing, the line follows up the northside bottomlands along the river to about 2 miles east of King Ranch. The bottomlands along Siuslaw River below 600 feet elevation are in the fog-belt zone of Coast Province, which is typified by the occasional Sitka spruce tree. From the vicinity of King Ranch on the Siuslaw, the line travels southerly along the divide between Siuslaw and Smith rivers and then westerly around the headwaters of Smith River.93
From the headwaters of South Fork Smith River about 5 miles northwest of Drain community, the line veers west along the divide between Smith River to the north and drainages flowing into Umpqua River to the south. This portion of the Umpqua system is in Willamette Province. About 4 miles north of Scottsburg, the line turns south to cross Umpqua River at Scottsburg community.36, 91 It ascends the ridge across the river from Scottsburg and goes southeast along the ridgetops to the big bends in Umpqua River west of Kellogg community. From there, it goes south along the ridgetop that divides drainages flowing to the east into Umpqua River from drainages flowing to the west into Coos and Coquille rivers.
The demarcation line crosses the Coos Bay Wagon Road west of Reston community, which is in Willamette Province, at 1,850 feet elevation and continues southwest at about 2,000 feet elevation.36, 91
About 7 miles southwest of Camas Valley community, in Willamette Province, the line of demarcation crosses Highway 42 along Middle Fork Coquille River at about 800 feet elevation. From there, the line ascends the ridge southeasterly to Chipmunk Ridge.51 It is near the southeast end of Chipmunk Ridge that Willamette, Coast, and Siskiyou provinces join.
The line of demarcation between Willamette and Coast provinces is based primarily on the elevation at which western hemlock grows. However, the line also is indicated by the general presence of such forested soils as Bellpine, Jory, Retner, and Bateman series, which typify Willamette Province, and Bohannon, Blachly, Preacher, and Digger series, which typify Coast Province.
Although the line of demarcation is based on the elevation at which western hemlock generally is common in forested uplands, it is interesting to note that at locations along the Coast Range crest where elevation is significantly below 1,700 feet, the hemlock line is at the pass on the summit. For example, where Sunset Highway (U.S. 26) crosses the summit into Nehalem River drainage, the province line is about 1,600 feet elevation. The Gales Creek Highway (Oregon 6) summit into Wilson River drainage also is about 1,600 feet elevation. At the community of Summit on the pass between Marys River and Yaquina River, the summit is about 730 feet elevation. On Highway 20 between Corvallis and Newport, the summit is about 800 feet elevation. On the Alsea Highway (Oregon 34), the summit is about 1,125 feet elevation. Farther south, the Willamette–Coast line of demarcation, based on the advent of western hemlock in forested uplands, is about 600 feet elevation where it crosses Siuslaw River, about 470 feet where it crosses Umpqua River, and about 800 feet where it crosses Middle Fork Coquille River. These rivers have major headwaters in Willamette Province. Furthermore, Umpqua River drains sizable watersheds in both Cascade and Siskiyou provinces.
Each of these river crossings and passes in the crest of the Coast Range where the advent of western hemlock signifies the line of demarcation between Willamette and Coast provinces apparently represents where the effects of the warmer, drier Willamette Valley climate are overcome by the more moist, cool coastal climate.
Willamette and Siskiyou Demarcation
From the junction of Willamette, Coast, and Siskiyou provinces near Chipmunk Ridge in southwest Douglas County, the line of demarcation between Willamette and Siskiyou provinces goes along the ridgetop north to the vicinity of Live Oak Mountain and continues northerly to circle the headwaters of Olalla Creek, which are in Siskiyou Province, and then south to Table Mountain. From there, the line meanders northeasterly along the ridgetop past Buck Mountain at about 2,500 feet elevation. About 4 miles northwest of Riddle, in Siskiyou Province, the line veers north and northwest by Big Baldy Mountain along the ridge separating drainages flowing west into lower Olalla Creek, in Willamette Province, from drainages in Siskiyou Province that are flowing north.
The line descends northwesterly to the edge of bottomlands along Olalla Creek at about 600 feet elevation and follows the southern border of these bottomlands north and east and along South Umpqua River, which is in Willamette Province at this location, to the bridge where Highway I-5 crosses South Umpqua River.36, 95
From the I-5 bridge across South Umpqua River, the line climbs the ridge northeast to Dodson Butte, Brushy Butte, and Lane Mountain. It is near Lane Mountain that the Willamette, Siskiyou, and Cascade provinces join.36, 51
The line of demarcation between Willamette and Siskiyou provinces, which is about 70 miles long, is not clear-cut in terms of soil or vegetation differences throughout its extent. Both provinces have arid, warm climates with Siskiyou being relatively more arid and warm than Willamette Province. The line was judged using data in the 1993 Preliminary General Soil Map, Douglas County, Oregon,95 which covers the area where the two provinces join. The line was drawn between upland soils that have been mapped definitely within Willamette Province to the north and upland soils that have been mapped in other areas definitely within Siskiyou Province. Upland soils definitely associated with Willamette Province include Oakland, Sutherlin, Nonpariel, Philomath, and Dixonville series. Upland soils definitely associated with Siskiyou Province include Speaker, Josephine, Lettia, and Beal series.
Broad vegetation characteristics differentiate between Willamette and Siskiyou provinces. For example, uplands below about 1,300 feet elevation in southern Willamette Province are typified by the common presence of bigleaf maple, Oregon white oak, scotchbroom, and some Pacific madrone. Equivalent uplands in Siskiyou Province are typified by California black oak, wedgeleaf ceanothus, and abundant madrone, which strongly dominates logged or otherwise disturbed forested areas. Certain segments of the demarcation line between Willamette and Siskiyou provinces demonstrate these vegetation comparisons.
Willamette and Cascade Demarcation
From the junction of Willamette, Siskiyou, and Cascade provinces near Lane Mountain about 10 miles east of Roseburg, the line of demarcation between Willamette and Cascade provinces goes north at about 1,500 feet elevation on north-facing slopes and at about 2,800 feet elevation on west- and south-facing slopes. The line is based on the advent of western hemlock in the forest which signifies the colder, more moist effective environment of Cascade Province as compared with Willamette Province.
The line travels east around the upper reaches of drainages into Little River and then northwest at about 2,000 feet elevation in the vicinity of Shivigny Mountain, which is in Cascade Province. It continues on northwesterly to cross North Umpqua River about 5 miles northeast of Glide, which is in Willamette Province, near Idleyld Park in the topographic gap where Rock Creek Fish Hatchery is. From this gap, the line heads north at about 2,000 feet elevation around the west slopes of Scott Mountain, Brown Mountain, and across Calapooya Divide. From near Calapooya Divide, the line goes north at about 1,800 feet elevation to the vicinity of Cottage Grove, extending up each major drainage that flows into Coast Fork Willamette River.
Northeast of Cottage Grove, which is in Willamette Province, the line goes generally north at about 1,800 feet elevation but extending up each major drainage that flows into Willamette River from the east. The line extends up Middle Fork Willamette River to about 17 miles south of Oakridge, which is in Willamette Province. The line extends up McKenzie River to near Belknap Springs; up Calapooia River to about King Camp; up South Umpqua River to about House Rock Forest Camp; up Middle Santiam River to just below Green Peter Dam; up North Santiam River to about 6 miles east of Mill City; up Little North Santiam River to about Elkhorn; up Clackamas River to about Fish Creek; and up Sandy River to about Brightwood.
The pattern of western hemlock growth, extending east up each major drainage that heads in the Cascade Mountains, signifies the effects of the warmer, drier Willamette climate extending up these valleys.
The line between Willamette and Cascade provinces near Firwood on Highway 26 in Clackamas County is at about 1,600 feet elevation. Farther north along Sandy River southeast of Portland, western hemlock occurs at about 1,400 feet elevation, including near Bridal Veil on the Columbia River. From the vicinity of Bridal Veil, the line of demarcation winds easterly along steep breaks of Columbia Gorge to pass west and south of Hood River Valley, which is in Willamette Province, at about 3,000 feet elevation. It continues to a point about 6 miles south of Parkdale in upper Hood River Valley. Near here, Willamette, Cascade, and The Dalles provinces join.
Although the line of demarcation between Willamette and Cascade provinces in Oregon is based primarily on the elevation at which western hemlock grows, the line also is indicated by the general occurrence of such forested soils as Honeygrove, Peavine, Bellpine, Philomath, Jory, Cazadero, Parkdale, Hoodview, and Bins, which typify Willamette Province, and by Klickitat, Kinney, Bohannon, Holderman, Henline, Aschoff, Bull Run, Divers, and Thader, which typify Cascade Province.
Willamette and The Dalles Demarcation
From the junction of Willamette, Cascade, and The Dalles provinces in Oregon, the line of demaracation between Willamette and The Dalles provinces runs along the ridge east of Hood River Valley and northeast down the ridge nearly to Highway I-84 along the Columbia River. Here it veers sharply upriver nearly to Mosier, which is in The Dalles Province. The towns of Hood River and Parkdale and the entire Hood River Valley are in Willamette Province; this is substantiated by the common presence of bigleaf maple, which does not grow in The Dalles Province.
The line between The Dalles and Willamette provinces in Oregon, which is about 30 miles long, is based on soil lines between Hood, Van Horn, Oak Grove, and Bins series, which typify Willamette Province in the vicinity of Hood River Valley, and Bald, Bodell, Frailey, and Ketchly series, which typify The Dalles Province in Oregon.89