Siskiyou and Klamath Demarcation
The line of demarcation between Siskiyou and Klamath provinces begins at the Oregon–California border in southwestern Klamath County on the east side of Klamath River. At this point, the line coincides reasonably well with the soils line between Pinehurst, Greystoke, and Bly soil mapping units, which represent Klamath Province, and Skookum–McMullin soil map unit, which represents Siskiyou Province.61
The line travels up Klamath River about 5 miles and then meanders west to the Jackson–Klamath county line at about 4,000 feet elevation where it goes northwest to pass close by Pinehurst on Highway 66. From the vicinity of Pinehurst, the line runs north up Jenny Creek and intersects the juncture of Siskiyou, Klamath, and Cascade provinces at about 5,000 feet elevation west of Brush Mountain, which is in Cascade Province.
The demarcation line between Siskiyou and Klamath provinces in this area is not based on soil maps. Rather, the line is the approximate boundary between the area vegetated with plant communities that include oak and wedgeleaf ceanothus, which typify Siskiyou Province in this area, and the mixed-pine–mixed-fir plant communities which typify Klamath Province.50 However, the Skookum–McMullin and McNull–McMullin soil map units are generally associated with plant communities that include white oak, ponderosa pine, and wedgeleaf ceanothus, which typify Siskiyou Province in this area, and the Pokegma–Woodcock soil map units which are associated with the mixed-pine and mixed-fir forest of Klamath Province in this area.61 Wedgeleaf ceanothus is a key indicator species of Siskiyou Province arid sites.
Siskiyou and Cascade Demarcation
The line of demarcation between Siskiyou and Cascade provinces wanders north from the vicinity of Brush Mountain at about 5,500 feet elevation to Fish Lake and along the western slopes of Mt. McLoughlin, which is in Cascade Province. The line continues north in the headwaters of Big Butte Creek and its tributaries, on to Rustler Peak, and then northwest to cross Rogue River and Highway 62 about 6 miles below the community of Prospect.
The line in this area is based on forested plant communities dominated by Douglas-fir, grand fir, sugar pine, and ponderosa pine, which represent Siskiyou Province, and forested plant communities dominated by mountain hemlock and true firs, which represent Cascade Province.50
From where the line crosses Highway 62 near Prospect, it runs northward around the headwaters of Elk Creek and South Umpqua River at about 4,000 feet elevation. The line turns west around headwaters of tributaries of South Umpqua River, which are in Siskiyou Province, at about 3,500 feet elevation. Consequently, the south- and west-facing slopes along South Umpqua River are in Siskiyou Province. In the vicinity of Tater Hill, the line veers northwest to White Rock at about 3,000 feet elevation and on to Lane Mountain where Siskiyou, Cascade, and Willamette provinces join.
The line between Siskiyou and Cascade provinces in the vicinity of South Umpqua River is based on the presence of western hemlock in Cascade Province forested plant communities and a lack of western hemlock in the more arid forested plant communities of Siskiyou Province. The line is supported in this area by such soil series as Holderman and Keel, which represent Cascade Province,91 and Lettia, Beal, Acker, Kanid, and Atring series, which represent Siskiyou Province.95
Siskiyou and Willamette Demarcation
From the junction of Siskiyou, Cascade, and Willamette provinces on Lane Mountain about 10 air miles east of Roseburg in Douglas County, the line of demarcation between Siskiyou and Willamette provinces goes southwest down the ridge to Brushy Butte and Dodson Mountain to cross South Umpqua River at the Highway I-5 bridge over the river about 4 air miles northwest of Myrtle Creek community.36, 95 From the Highway I-5 bridge, the line follows the southern border of bottomlands along South Fork Umpqua River and Olalla Creek at about 600 feet elevation. From there it veers south up the ridge separating drainages flowing west into lower Olalla Creek, in Willamette Province, from drainages flowing north, which are in Siskiyou Province, to Big Baldy Mountain about 4 air miles northwest of Riddle community.
From Big Baldy Mountain the line goes southwest along the ridgetop at about 2,500 feet elevation past Buck Mountain to Table Mountain where it curves north to circle the headwaters of Olalla Creek, which is in Siskiyou Province. The line follows the ridge from Live Oak Mountain southwest to Chipmunk Ridge, which is where the junction of Siskiyou, Willamette, and Coast provinces lies.
The line between Siskiyou and Willamette provinces, which is about 70 miles long, is not always clear-cut in terms of soil or vegetational differences. Both provinces have arid, warm climatic conditions though Siskiyou is relatively more arid and warmer than Willamette Province. The line was selected by using data shown on the 1993 Preliminary General Soil Map, Douglas County, Oregon95 which covers the area where these 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 occurrence 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.
Siskiyou and Coast Demarcation
From the junction of Willamette, Siskiyou, and Coast provinces in the vicinity of Chipmunk Ridge in southwestern Douglas County, the line of demarcation between Siskiyou and Coast provinces goes south at about 3,000 feet elevation to Dutchman Butte. It follows Hayes Ridge southwesterly and south to Ninemile Mountain and continues southwesterly at about 3,000 feet elevation to north of Kelsey Peak in northeastern Curry County. From there, the line wanders west to Big Meadows vicinity and then north, west, and southwest at about 3,000 feet elevation around the upper Mule Creek watershed. It follows Panther Ridge southwesterly at about 2,000 feet elevation close to the Coos–Curry county line.
From this point, the line extends south along the east slopes of Ophir Mountain and Brushy Mountain at about 2,000 feet elevation. In the vicinity of Lake of the Woods Mountain the line goes southwest to Soldier Camp Mountain, Second Prairie Mountain, and First Prairie Mountain while decreasing in elevation from about 2,000 feet at Soldier Camp Mountain to about 1,200 feet in the vicinity of Lobster Hill just north of Rogue River.51
The line in northeastern and north-central Curry County is based primarily on the elevation at which western hemlock is a common component of forested uplands in Coast Province, compared to the common appearance of tanoak, madrone, and other plant species that signify warmer and drier conditions typifying the western part of Siskiyou Province. The line also is indicated by the general presence of such forested soils as Preacher, Bohannon, Digger, and Umpcoos, which typify Coast Province, 60and 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 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 between provinces from this area south to the Oregon–California border. Several sharp bends in Rogue River near Lobster Hill apparently hinder the upper boundary of the normal fog zone from extending farther upriver. The line of demarcation, therefore, crosses Rogue River between Lobster Hill and Skookumhouse Butte.
The line—the upper boundary of the coastal fog zone—continues at about 1,200 feet elevation around the headwaters of Quosatana Creek and west around Kimball Hill. The line goes southwest, somewhat parallel to Rogue River, and then south at about 1,200 feet elevation. It winds 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, which is a tributary of Rogue River, and south to the Oregon–California border, thedemarcation line is based on the presence of Sitka spruce, red alder, Douglas-fir, western hemlock, and other species that typify the cool, moist fog zone coastal climate as compared to the common occurrence of tanoak, Pacific madrone, and related species that signify the warmer, drier conditions typifying Siskiyou Province. This line also is indicated by the general presence of such soils as Bosland, Floras, Millicoma, and Reedsport, which typify Coast Province in this area, and Fritsland, Bravo, Mislatnah, and Pollard soil series which typify Siskiyou Province in this area.56