Coast and Willamette Demarcation
The line of demarcation between Coast and Willamette provinces begins just west of Rainier on the bank of the Columbia River in Columbia County. From there it meanders west along the tops of steep slopes overlooking the Columbia 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 of demarcation 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 goes 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 to cross 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 goes southeast at about 1,750 feet elevation to the Tillamook–Washington county line. It cuts 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 meander south around the headwaters of drainages flowing east into the Tualatin and North Yamhill rivers.
Northwest of McMinnville, the demarcation line makes a huge swing west at about 1,700 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 demarcation 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 southwestern Polk County, the line descends the ridge southeasterly to cross the Luckiamute River at about 650 feet elevation. It ascends Cougar Ridge and then meanders south along the crest of the Coast Range. The Coast Range descends on the narrow divide between Marys River and Yaquina River to about 730 feet elevation at the community of Summit, which is about 5 miles northwest of Blodgett on Highway 20.
From the community of Summit, the demarcation 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 of demarcation runs south along the crest of the Coast Range to Marys Peak where it turns north and east around Marys Peak at about 1,700 feet elevation. The line crosses the pass on Alsea highway (Oregon 34) at about 1,125 feet elevation and continues southeast up the ridge and around the east slopes of Flat Mountain at about 1,750 feet elevation. From there the line continues south at about the same 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 demarcation line 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 southeasterly along the crest of the Coast Range and 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 crossing on the river, 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 the Coast Province, which is typified by the presence of occasional Sitka spruce trees. From the vicinity of King Ranch on the Siuslaw, the line travels south along the divide between Siuslaw and Smith rivers and then west 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 veers south to cross Umpqua River at Scottsburg community.36, 71 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 and drainages flowing to the west into the Coos and Coquille rivers.
The line crosses the Coos Bay Wagon Road west of Reston community, which is in Willamette Province, at 1,850 feet elevation and continues southwesterly at about 2,000 feet elevation.36, 91
About 7 miles southwest of Camas Valley community, which is in Willamette Province, the line 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 The junction of the Coast, Willamette, and Siskiyou provinces is near the southeast end of Chipmunk Ridge.
The line of demarcation between Coast and Willamette provinces is based primarily on the elevation at which western hemlock is common. This line also is supported by the general occurrence of such forested soils as the Bellpine, Jory, Retner, and Bateman series, which typify Willamette Province, and by the Bohanon, Blachly, Preacher, and Digger series which typify Coast Province.
It is interesting to note that at locations along the crest of the Coast Range where the 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 the Nehalem River drainage, the province line 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 Coast–Willamette 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 the 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, apparently marks where the effects of the warm, arid Willamette Valley climate are overcome by the more moist, cool coastal climate.
Coast and Siskiyou Demarcation
From the juncture of Coast, Willamette, and Siskiyou provinces near Chipmunk Ridge in southwestern Douglas County, the line of demarcation between Coast and Siskiyou provinces goes south at about 3,000 feet elevation to Dutchman Butte. It follows Hayes Ridge southwesterly and southward to Ninemile Mountain and continues southwesterly at about 3,200 feet elevation to north of Kelsey Peak in northeastern Curry County. From there, the line runs west Big Meadows vicinity and then north, west, and southwesterly at about 3,000 feet elevation around the upper Mule Creek watershed. It follows Panther Ridge southwesterly at about 2,800 feet elevation close to the Coos–Curry county line.
From this location, the line extends south along the east slopes of Ophir Mountain and Brushy Mountain at about 2,800 feet elevation. In the vicinity of Lake of the Woods Mountain the line runs southwest to Soldier Camp Mountain, Second Prairie Mountain, and First Prairie Mountain. Elevation decreases from about 2,800 feet at Soldier Camp Mountain to about 1,200 feet in the vicinity of Lobster Hill just north of Rogue River.51
The demarcation line in northeastern and north-central Curry County is based primarily on the elevation at which western hemlock is common in forested uplands in Coast Province, as compared to the common occurrence of tanoak, madrone, and other plant species that signify the warmer and drier conditions that typify the western portion of Siskiyou Province. This line of demarcation also is supported by the general occurrence of such forested soils as Preacher, Bohannon, Digger, and Umpcoos, which typify Coast Province,60 and the soil series Atring, Kanid, Acker, Beekman, Pollard, and Vermisa, which typify Siskiyou Province in this vicinity.56
In the vicinity of Lobster Hill the line of demarcation between Coast and Siskiyou provinces intersects the upper boundary of the normal coastal fog zone at about 1,200 feet elevation. This upper boundary coincides with the line of demarcation from this area south to the Oregon–California border. Several sharp bends in the Rogue River near Lobster Hill apparently hinder the fog from extending farther upriver. The line of demarcation, therefore, crosses the Rogue River between Lobster Hill and Skookumhouse Butte.
The line, which is the upper boundary of coastal fog zone, continues at about 1,200 feet elevation around the headwaters of Quosatana Creek and west around Kimball Hill. The line runs southwesterly somewhat parallel to the Rogue River and then south at about 1,200 feet elevation. It travels up and around the headwaters of Hunter Creek, then west of Sundown Mountain, up and around headwaters of Pistol River and its tributaries, of Chetco River and its tributaries, and of Winchuck River and its tributaries at about 1,200 feet elevation.51 It crosses from Oregon into California about 8 air miles east of the Pacific Ocean.
From the vicinity east of Lobster Creek, a tributary of the Rogue River, and south to the Oregon–California border, the line of demarcation between Coast and Siskiyou provinces is based on the occurrence of Sitka spruce, red alder, Douglas-fir, western hemlock, and other species that typify the cool, moist fog zone coastal climate. By comparison, the common occurrence of tanoak, Pacific madrone, and related species signify the warmer, drier conditions that typify Siskiyou Province. This line also is supported by the general occurrence of such soils as Bosland, Floras, Millicoma, and Reedsport, which typify Coast Province in this area, and Fritsland, Bravo, Mislatnah, and Pollard which typify Siskiyou Province in this area.56
From the California border north, the upper boundary of the normal coastal fog zone is at about 1,200 to 1,400 feet elevation in the drainages of Winchuck, Chetco, Pistol, and Rogue rivers where it constitutes the line of demarcation between Coast and Siskiyou provinces.
From the vicinity of the Rogue River north to Humbug Mountain, the upper boundary of the coastal fog zone remains at about 1,200 feet elevation. However, it does not constitute the Coast Province boundary in this area because east of the fog zone in this area are forested uplands in which western hemlock is common. Western hemlock is a key indicator species that typifies uplands of Coast Province from this vicinity north to the Columbia River.
North from Humbug Mountain, the upper level of the fog zone lowers to about 800 feet elevation. 51 Still farther north, the fog zone is up to about 500 to 600 feet elevation in the valleys of major drainages such as the Alsea, Yaquina, and Salmon rivers. There, the fog zone boundary is represented by occurrence of Sitka spruce, a key indicator species of the cool, moist fog zone.25, 34, 35, 36, 44, 45, 46
Changes from south to north in the elevation of the upper boundary of the coastal fog zone is likely caused by changes in coastal climatic conditions. Although not substantiated by available weather data, observations of onshore storm patterns have been that stormy weather south from Cape Blanco often is less severe than it is to the north, which may help account for a cooler, more moist annual climate north along the coast. The pattern of plant community composition from south to north supports this concept.
The coastal fog zone’s upper boundary is the distance that fog normally penetrates major coastal river systems having headwaters at higher elevations in the Coast Range. However, on major coastal rivers that have headwaters at low elevations in the Willamette Valley, such as the Umpqua, the normal fog zone penetrates only to the point that the warm, dry climate of the Willamette Valley resists fog penetration up the drainage. On the upper Umpqua River, for example, the line between Coast and Willamette provinces crosses the river from north to south at Scottsburg, which has an elevation of 47 feet. The Willamette Valley’s type of vegetation— representing a warm, dry climate—is very apparent to the east of the line of demarcation at Scottsburg.
The differences between the coastal fog zone north from Humbug Mountain and that from Humbug Mountain south to the California border suggests that further study to the south, into California, might substantiate the existence of a Northern Coast Ecological Province in California. The coastal fog zone area south from Humbug Mountain may be a transition between a Sitka spruce/western hemlock/shore pine/Douglas-fir-dominated vegetation to the north and a tanoak/Douglas-fir/coast redwood-dominated vegetation to the south. However, based on current concepts, the coastal fog zone south from Humbug Mountain, although somewhat different from that north of Humbug Mountain in terms of vegetation and soils, has been included in the Coast Ecological Province of Oregon.