Cascade and Willamette Demarcation
The juncture between Cascade, The Dalles, and Willamette provinces occurs about 6 miles south of Parkdale in Upper Hood River Valley and east of Highway 35, at an elevation of about 3,000 feet. Starting from this location, the line meanders northwest to the Columbia River Gorge where it continues along steep breaks of the gorge. Hood River Valley and Columbia Gorge are in Willamette Province. 44 The line of demarcation between Cascade and Willamette provinces is signified by the appearance of western hemlock in the Cascade forests.
North of Larch Mountain in eastern Multnomah County, the line of demarcation gradually drops to about 1,400 feet in the vicinity of Bridal Veil, and from this area the line veers south at about that elevation. As the line goes south, it follows eastward up the south-facing slopes of each major drainage that heads in the Cascade Mountains and returns westward along the base of north-facing slopes of that same drainage.
This path reflects a significant pattern in the elevations at which western hemlock signifies the Cascade Province. Obviously, the pattern is an effect of the warm arid climate of Willamette Valley which extends up these valleys. Along the base of north exposures, western hemlock is at about 1,200 feet, and that elevation on north exposures in drainages does not vary significantly from the Sandy River southeast of Portland south to the North Umpqua River northeast of Roseburg. Western hemlock occurs at about 1,200 feet elevation on north-facing slopes of each major drainage in this part of Oregon.
However, in this same area on south-facing slopes (which represent increasingly drier and warmer situations) western hemlock rises in elevation from north to south. For example, along the Sandy River southeast of Portland, western hemlock occurs at about 1,400 feet elevation on south-facing slopes. But, when the line of demarcation continues southward from the vicinity of Firwood on Highway 26 in Clackamas County, the appearance of western hemlock on south exposures rises to about 1,600 feet. Farther south along South Santiam River, western hemlock occurs at about 1,800 feet elevation on south-facing slopes.45
Western hemlock on south-facing slopes and on climate-climax positions probably occurs at about 1,800 feet elevation along the Santiam, Calapooya and McKenzie river drainages. However, farther south along the Middle Fork Willamette River, the occurrence of western hemlock rises to about 2,000 feet elevation on both south- and north-facing slopes.
In this north-to-south transition, the line of demarcation between Cascade and Willamette provinces extends east, up the Sandy River to about Brightwood; up the Clackamas River to about Fish Creek; up the Little North Santiam to about Elkhorn; up the North Santiam River to about 6 miles east of Mill City; up the Middle Santiam River to just below Green Peter Dam; up the South Santiam River to about House Rock Forest Camp; up the Calapooya River to about King Camp; and up the McKenzie River to about Belknap Springs.
Near Belknap Springs, the eastern boundary of Willamette Province is close to the western boundary of Mazama Province. A narrow strip connects that portion of Cascade Province north of the McKenzie River and the portion south of it.
The line of demarcation between Cascade and Willamette provinces east of Cottage Grove, which is in Willamette Province, lies at about 2,000 feet elevation on west-facing slopes. It meanders up and back down various minor drainages between there and the North Fork Umpqua River. The line crosses North Fork 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 ascends south up the ridge to about 2,800 feet elevation on south-facing slopes in the vicinity of Shivigny Mountain, which is in Cascade Province. From this area around the upper reaches of Little River, hemlock occurs at about 1,500 feet elevation on north-facing slopes and at about 2,800 feet on west- and south-facing slopes. Unpublished studies36 indicate that areas above about 3,600 feet in Cascade Province are forested mainly by true fir and mountain hemlock. These high-elevation areas have been referred to locally as the High Cascades, and they are components of Cascade Province.
Cascade and Siskiyou Demarcation
In the vicinity of Lane Mountain about 10 miles east of Roseburg, which is in Willamette Province, lies the junction of Cascade, Willamette, and Siskiyou provinces.36,50 In this vicinity, the drainages into South Umpqua River are southwesterly which exposes the generally south-facing headwaters of the drainages to the arid, hot climate that typifies Siskiyou Province. Consequently, the line of demarcation between Cascade and Siskiyou provinces generally follows around the headwaters of these drainages at about 3,000 feet on south- and west-facing slopes.
In the headwaters of South Umpqua River and its tributaries, the line of demarcation wanders south at about 4,000 feet elevation. It continues along the west slopes of Quartz Mountain and then southerly along the west slopes of Bald Mountain to cross the Rogue River about 6 miles below the community of Prospect, which is in Mazama Province. In this area the narrow ash flow out of Mt. Mazama (Crater Lake), which extends southwest between the communities of Union Creek and Prospect, creates a narrow strip connecting the portions of Cascade Province that lie to the north and the south of Crater Lake.
From about 6 miles below the community of Prospect, the line meanders southeast at about 4,000 feet elevation. It gradually rises in elevation through the headwaters of drainages into Rogue River, Big Butte Creek and Little Butte Creek. Mt. McLoughlin is in Cascade Province. Fish Lake at the head of Little Butte Creek is in Siskiyou Province. The juncture of Cascade, Siskiyou, and Klamath provinces is in the vicinity of Brush Mountain in southeastern Jackson County at about 5,500 feet elevation.
Cascade and Klamath Demarcation
The line between Cascade and Klamath pProvinces runs southeast at about 5,500 feet elevation around the headwaters of Jenny Creek in southwestern Klamath County and on to the south slopes of Buck Mountain. From Buck Mountain, the line turns north on the east side of Buck Peak, Mt. Harriman, Pelican Butte, Lather Mountain, and Klamath Point. Each of these mountains is in Cascade Province. The juncture of Cascade, Klamath, and Mazama provinces is near Klamath Point.
Cascade and Mazama Demarcation
From that juncture, the line between Cascade and Mazama provinces goes northwest about 1 to 3 miles south of and somewhat paralleling Highway 62, to the vicinity of Union Creek community. In this area, the Mazama Province extends southerly in a valley 2 to 3 miles wide lying on each side of Highway 62 from Union Creek south to Prospect. This narrow extension of Mazama Province appears to be a large ash flow along the upper Rogue River extending southwest from the main pumice mantle near Crater Lake. The soil typifying this ash-flow extension of Mazama Province is Alcot series. Soils in the adjacent Cascade province are Freezner and Geppart.68
From the vicinity of Union Creek community, the line runs north across the divide between the Rogue River and North Umpqua River watersheds just east of Buckneck Mountain. From there, it follows northerly down Clear Creek, across the plateau at Toketee airstrip, and across North Umpqua River below Toketee Reservoir. It then heads northeast to cross the divide between North Umpqua River and the headwaters of the Middle Fork Willamette River about 5 miles west of the Cascade Range crest.91
From the headwaters of the Middle Fork Willamette River, the line between Cascade and Mazama provinces runs north around the west side of Bear Mountain to Salt Creek canyon. There, the Southern Pacific railroad climbs a switchback out of Salt Creek to pass over the summit of Cascade Mountains just west of Odell Lake, which is in Mazama Province. The line of demarcation goes north, to the west of Waldo Lake, and then east of Moolack Mountain and around the headwaters of the South Fork McKenzie River.93
The 1970 General Soil Map of Linn County 80 does not provide soil information in the mountainous eastern portion of the county. Therefore, the line of demarcation between Cascade and Mazama provinces in that area is drawn on the basis of topographic features of the line on maps to the south of this area. In Lane and Douglas counties, the mapped pumice-mantle boundary is primarily along a major topographic change in the landscape: a relatively undulating or sloping area to the east of the line, which typifies Mazama Province in that area and, to the west, relatively steep mountainous terrain which represents the sharp dendritic drainage pattern of Cascade Province.
Some pumice from the eruption of Mt. Mazama likely fell in the Cascade Mountains west of the current pumice mantle. However, because of the steep dendritic drainage pattern representing headwaters of numerous drainages into the Willamette River, these pumice deposits probably have been washed downstream or may still be in isolated deposits mainly on steep north-facing slopes within Willamette Province.
Using the previously described topographic feature as a guide, the line of demarcation between Cascade and Mazama provinces is predicted to run north from the headwaters of the South Fork McKenzie River on around the headwaters of the McKenzie and South Santiam rivers near Fish and Lava lakes, about where Highway 20 crosses the pass. From there, the predicted line veers northeast to cross Highway 22 about 4 to 5 miles northwest of Santiam Junction. The line probably continues northeast into Jefferson County north of Three Fingered Jack peak and to where Jefferson Creek joins Metolius River. In that area, Cascade, Mazama, and The Dalles provinces meet.
The demarcation line between Cascade and Mazama provinces in Douglas, Lane, and Linn counties is based on soil lines between Holderman and Keel soil series, which typify Cascade Province, and Winopee and Shukash soil series, which typify Mazama Province.79 Farther north, in western Jefferson County, the soil series in Cascade Province may be Howash and Mackatie, which typify Cascade Province on the Warm Springs Indian Reservation96; soil series in adjacent Mazama Province include Lapine, Shanahan, Deschutes, and Steiger.70
Cascade and The Dalles Demarcation
From the juncture of Cascade, Mazama, and The Dalles provinces in western Jefferson County, the line of demarcation between Cascade and The Dalles provinces runs north along the eastern slopes of Cascade Mountains at about 4,500 feet elevation—approximately the elevation at which western hemlock becomes a significant component of forested plant communities in this area.
In southwestern Wasco County, the demarcation line drops to about 4,000 feet elevation as it goes north. Western hemlock’s occurrence at lower elevations in northern than in southern Oregon is seen on both east and west slopes of the Cascade Mountains as well as along the east slopes of the coast range. Apparently, this is due to an overall warmer climate to the south which causes western hemlock to occur at high elevations.
The line meanders north at about 3,000 feet elevation to an area near the southeastern corner of Upper Hood River Valley where Cascade, The Dalles, and Willamette provinces join.