Mazama and John Day Demarcation
The first point is at the north boundary near where Deschutes River exits Mazama Province at what is locally known as Lower Desert, which is where The Dalles, John Day, and Mazama provinces join. From there, the line of demarcation between the Mazama and John Day provinces goes southeast along the Crooked River past Smith Rock and continues across the plateau crossing Highway 126 about 4 miles east of the community of Powell Butte. Powell Butte, Redmond, and Terrebonne are in Mazama Province; Smith Rock, Gray Butte, Prineville, and nearly all of the National Grasslands are in John Day Province. At the mouth of Crooked River canyon about 6 miles south of Prineville, the demarcation line between Mazama and John Day provinces essentially follows the west canyon rim of Crooked River to the vicinity of its confluence with Bear Creek. From there it continues south along the east side of Bear Creek and then southeast along the breaks of Bear Creek. About 5 miles north of Brothers the line turns east at about 5,000 feet elevation to the area north of Grassy Butte.
Elevation is not as significant in demarcation between Mazama and John Day provinces as it is between some other provinces. This is because Mazama Province is an ancient landscape covered by an aeolian pumice mantle that is not necessarily affected by elevation or landform. It should be noted, however, that the pumice deposit at the perimeter of the pumice mantle likely was thinner than toward the interior of the fallout area. Unpublished field studies indicate that where about 8 to 10 inches or more of pumice lies over buried soils, herbaceous vegetation resembles that of the arid nonforested portion of Mazama Province; i.e., bluebunch wheatgrass/Idaho fescue. Less than 8 to 10 inches pumice mantle over buried soils produces herbaceous vegetation typical of High Desert Province; i.e., bluebunch wheatgrass/Thurber needlegrass. Obviously, these are not clearcut differences out on the land because they occur within a belt of demarcation.32
It also should be noted that Mazama aeolian pumice falling on existing hilly uplands in a relatively thin mantle along the perimeter of the fallout pattern likely was washed into adjacent valleys and drainages by subsequent precipitation. Therefore, hilly uplands in the vicinity of the line of demarcation between Mazama and John Day provinces help establish the location of this line; generally, the flatter land is in Mazama and hilly uplands are in John Day Province.
North of Hampton Butte the line turns south more or less along the boundary between the basin and uplands. Southwest of Hampton Butte, Mazama, John Day, and High Desert provinces join about 5 miles northwest of Hampton.
The line between the provinces is based on soil lines between Deschutes, Shanahan, and Lapine soil series, which typify Mazama Province, and Agency, Madras, and Simas soil series which typify John Day Province.70
Mazama and High Desert Demarcation
The line between Mazama and High Desert provinces crosses Highway 20 about 8 miles northwest of Hampton. From there it wanders southwest along the north portion of Devils Garden and continues southwest by Cabin Lake Ranger Station, which is very near the line, and on to Hole-in-the-Ground, which is in Mazama Province. This section of the line is more a belt in which the pumice mantle to the west is generally 8 to 10 inches or more thick over buried soil and represents Mazama Province. The area to the east of this belt generally has less than 8 to 10 inches of pumice mantle, if any, and is in High Desert Province.
From Hole-in-the-Ground, the line heads south at about 4,500 feet elevation. Where it crosses Highway 31 below the rimrocks northwest from Horse Ranch, the highway roadcut reveals an ancient lakeshore terrace of layered lacustrine materials, which signifies the boundary of High Desert Province.
After the line crosses Highway 31 northwest of Horse Ranch, it runs south almost parallel and about 1 to 2 miles west of the highway for about 10 miles until it veers south to the vicinity of Halfway Lake and the eastern portion of Antelope Flat. From this point, the line goes east across Buck Creek and Bridge Creek; at this point, at about 4,900 feet elevation, Mazama, High Desert, and Klamath provinces join.
The line between Mazama and High Desert provinces is based on soil lines between Shanahan and Lapine soil series, which typify Mazama Province, and Gardone, Floke, and Olson soil series which typify High Desert Province.84
Mazama and Klamath Demarcation
The line of demarcation between Mazama and Klamath provinces runs south to the area west of Thompson Reservoir, which is in Klamath Province, then around Sycan Butte, which is in Mazama Province, and along the east side of Sycan Marsh, also in Mazama Province.84 From about 5 miles southwest of Sycan Marsh on the Sycan River, the line turns east and travels northeast across the headwaters of Sycan River and then southeast in the vicinity of Winter Ridge. From the south portion of Winter Ridge, the line goes south across upper Elder Creek to west of Campbell Lake and south of Deadhorse Rim where it turns west along the south-facing slopes of Gearhart Mountain, in Mazama Province.84
From the area south of Gearhart Mountain, the line runs west to North Fork Sprague River. From there it snakes its way west more or less near the north boundary of Sprague River valley. Ferguson Mountain is in Mazama Province. From the vicinity of Knott Tableland, which is in Klamath Province, the line heads northwest, passing about 5 miles north of Sprague River community, which is in Klamath Province. From there, it goes south and west to the vicinity of Chiloquin and south to Lobert Junction.
From the vicinity of Lobert Junction on Highway 97, the line runs north along the east side of Agency Lake to the vicinity of Klamath Agency, which is in Mazama Province, then northwesterly to about 4 miles west of Fort Klamath along the east side of Klamath Point. It is in this vicinity that the juncture between Mazama, Klamath, and Cascade provinces lies.
The line of demarcation between Mazama and Klamath provinces is based on soil lines between Lapine, Shanahan, and Kirk–Chock soil series, which typify Mazama Province, and Woodcock, Hart, and Lorella soil series, which typify Klamath Province.77
Mazama and Cascade Demarcation
From the junction of Mazama, Klamath and Cascade provinces northwest of Fort Klamath, the line of demarcation between Mazama and Cascade provinces goes northwest, then about 1 to 3 miles south and somewhat paralleling Highway 62 to the vicinity of Union Creek community. From this point, 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 series typifying this ash flow extension of Mazama is Alcot. Soils in the adjacent Cascade Province are Freeznor and Geppert.68
From the vicinity of Union Creek community, the line goes north, crossing the divide between Rogue River and the 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 travels northeasterly to cross the divide between North Umpqua River and the headwaters of Middle Fork Willamette River about 5 miles west of the Cascade Range crest.91
From the headwaters of Middle Fork Willamette River, the line goes north around the west side of Bear Mountain and to the Salt Creek canyon where the Southern Pacific Railroad switchbacks out of Salt Creek to pass over the summit of the Cascade Mountains just west of Odell Lake, which is in Mazama Province. The line wanders northward west of Waldo Lake and then east of Moolack Mountain and around the headwaters of South Fork McKenzie River.93
The Linn County soil map 80 does not provide soil information in the mountainous east portion of the county. Therefore, the line of demarcation between Mazama and Cascade provinces in that area is drawn on the basis of topographic features apparent on maps showing the line of demarcation to the south of this area. In Lane and Douglas counties, the mapped pumice-soil boundary is primarily along a major topographic feature: a relatively undulating or sloping area to the east, which typifies the pumice-soil (Mazama) area, and relatively steep mountainous terrain to the west (Cascade) which represents the sharp dendritic drainage pattern of tributaries into the Willamette River.
It seems reasonable to assume that some pumice from the eruption of Mt. Mazama fell in the Cascade Mountains to the west of the current pumice mantle. However, because of the steep dendritic drainage pattern of headwaters of numerous drainages into the Willamette River, these pumice deposits probably have been washed downstream or may still lie in isolated deposits mainly on steep north-facing exposures within Cascade Province.
Using the previously described topographic feature as a guide, the demarcation line is predicted to run north from the headwaters of South Fork McKenzie River on around the headwaters of 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 on to about where Jefferson Creek joins Metolius River. At that point, Mazama, Cascade, and The Dalles provinces join.
The line of demarcation between Mazama and Cascade provinces in Douglas, Lane, and, likely, Linn counties is based on soil lines between Winopee and Shukash soil series, which typify Mazama Province, and Holderman and Keel series, which typify Cascade Province.91, 93 At the northern boundary of Mazama Province, the soil series in Mazama Province may be much like Lapine, Deschutes, Shanahan, and Steiger pumicey soils.62 Soil series in Cascade Province in this area may be Howash and Mackatie, which typify Cascade Province on the Warm Springs Indian Reservation.96
Mazama and The Dalles Demarcation
Where Jefferson Creek joins Metolius River in southwestern Jefferson County, Mazama, Cascade, and The Dalles provinces join. From that point, the line of demarcation between Mazama and The Dalles provinces follows south along Green Ridge to the east side of Black Butte, which is in Mazama Province. From there it meanders east and northeast to Lower Desert, which is the junction of Mazama, The Dalles, and John Day provinces.70