Mazama Ecological Province





Mazama Ecological Province, in central Oregon, is entirely within the state. It is the area covered by an aeolian deposit of pumice and other volcanic materials spewed over the countryside when Mt. Mazama erupted explosively about 6,500 years ago. Due to prevailing southwesterly winds, the pumice mantle lies primarily north and east of Crater Lake, which is in the caldera of Mt. Mazama. The mantle extends about 120 miles north from Crater Lake to the area north of Sisters and Redmond in northern Deschutes County, about 110 miles northeast to the vicinity of Brothers in northeast Deschutes County, and about 60 miles southeast to Gearhart Mountain in western Lake County. The pumice mantle extends only about 6 miles southwest of Crater Lake. Also, the western edge of the mantle is about 10 miles west of Crater, Diamond, Crescent, and Odell lakes and continues northerly about 5 miles west of the Cascade crest.

Other volcanic activities and eruptions, such as those related to Newberry Crater, as well as glacial actions have created areas within this province consisting of basaltic, andesitic, rhyolitic, and tuffaceous deposits, cinders, and glacial till.

The province covers about 5.1 million acres mainly in Deschutes, Klamath, and Lake counties east of the crest of the Cascade Range. Minor portions of the province are near the Cascade crest in northeast Jackson County, eastern Douglas and Lane counties, and southeast Linn County and in the southwest corner of Jefferson County. Communities in the province include Sisters, Redmond, Powell Butte, Brothers, and Bend in the northern part; Lapine, Gilchrist, Crescent, and Chemult along Highway 97 in the central part; and Chiloquin and Fort Klamath in the south.



Mazama Province is characterized by sloping and undulating plateaus in the northern and northeastern portions and by hilly to mountainous topography interspersed with basins throughout most of its interior and western portion. Innumerable large and small buttes, cones, ridges, and mountains formed by volcanism are interspersed across the landscape. Fields of raw lava and pumice are common.

The lowest elevation in the province is about 2,700 feet which is near the northern province border, south of The Peninsula where Deschutes and Crooked rivers join. Most of the province lies between 4,000 and 5,000 feet elevation. South Paulina Peak in the northeast part of the province is 8,010 feet elevation; Gearhart Mountain in the southeast part is 8,390 feet elevation. Yamsey Butte east of Klamath Marsh in the south of the province is 8,085 feet elevation. Many peaks along the western part of the province, which includes the Cascade Range, exceed 8,000 feet elevation. (Elevations are from USGS 1:250,000 topographic maps.) They include Mt. Scott just east of Crater lake, 8,339 feet; Mt. Bailey just west of Diamond Lake, 8,363 feet; Bachelor Butte southwest of Bend, 9,040 feet; and Broken Top west of Bend, 9,165 feet. The crest of the Cascade Range that is within Mazama Province is marked by spectacular peaks including Mt. Thielsen, 9,182 feet; Diamond Peak, 8,744 feet; South Sister, 10,430 feet; Middle Sister, 10,053 feet; and North Sister, 10,009 feet (Fig. 31).

Figure 31: View of Mr. Thielson over snow-covered pumice desert as seen from Crater Lake

The western part of the province is noted for its numerous mountain lakes and recreation areas (Fig. 32). Diamond, Lemolo, and Waldo lakes lie west of the Cascade crest; Crescent, Summit, Odell, Wickiup, Davis, Crane Prairie, Cultus, Sparks, and others lie east of the crest. All are in Mazama Province. Klamath Marsh and Sycan Marsh are two significant wetlands in the province. The major drainage from the province is through the Deschutes River which flows north to exit the province near The Peninsula northwest of Redmond (Fig. 31).

Figure 32: Mt. Thielsen as viewed from Diamond Lake, one of the many natural lakes that receive heavy recreational use in Mazama Province, Oregon



The primary upland soils typifying Mazama Province have been developed in various combinations of aeolian pumice and volcanic ash overlying basaltic bedrock or ancient soils at varying depths from about 8 to 10 inches up to about 15 feet.

Major soil series typifying uplands include Deschutes and Steiger, which generally are relatively thick deposits of aeolian pumice. Lapine and Shanahan soil series generally are aeolian pumice overlying buried loamy soil at varying depths to about 40 inches.

Certain major soil series typify bottomland or topographic basins. Wickiup series is a deep, imperfectly drained, very gravelly, coarse pumicy soil that occurs in basins and draws in forested uplands. Skellock series is a deep, gravelly, sandy loam that occurs on the fringe of marshy areas. Lodgepole pine is very likely the climax tree species on Wickiup and Skellock soils because of its tolerance for imperfectly drained, cold sites. The Dilman series is a black, clayey, imperfectly drained soil typically associated with flood plains, such as along Deschutes River, and with mountain meadows such as Long Prairie south from Lapine. Pumicey soils on marshes, such as Sycan and Klamath marshes, include soil series such as Chinchallo, Yamsay, and Moyina, which are black, poorly drained soils that may have layers of organic matter in the profile.

A very small part of Mazama Province is used for irrigated pasture and cropland; such agricultural use is restricted primarily to the area bounded by the communities of Sisters, Redmond, and Pilot Butte on the north and by Alfalfa and Bend on the south. Irrigated fields within this area are somewhat scattered, isolated by low ridges and mounds of basalt bedrock and rubble. The primary soil series being irrigated is Deschutes sandy loam.



Twelve official weather stations represent a cross-section of Mazama Province. Average elevation of the five stations in Deschutes County, which constitute the northern part of the province, is about 3,900 feet; average elevation of seven stations in Klamath County to the south is about 4,200 feet. In contrast to this relatively insignificant difference in elevation from north to south within the province, the average annual precipitation in Deschutes County is 14.7 inches but 38.6 inches in Klamath County. Sixty-seven percent of annual precipitation in the north portion falls during winter (November through March), 26% during the growing season (April through July). In the south, 77% of annual precipitation is in winter and 19% in the growing season. The north part of the province apparently is slightly warmer than the south. Maximum and minimum temperatures in January are 39.2 and 15.4°F, respectively, in the north compared to 36.1 and 14.5°F, respectively, in the south. Growing season maximum and minimum temperatures follow this pattern: 69.4 and 34.3°F in the north compared with 65.1 and 32.5°F in the south.

A precipitation map 53 clearly shows the broad precipitation patterns in most of Mazama Province and the Cascade Range’s contribution to overall precipitation. The map shows 145 inches annual precipitation in the Three Sisters area west of Bend, which is the highest precipitation in the province. The map also shows about 10 inches annual precipitation at Brothers in the northeast part of the province. Johnsgard’s data show 8.6 inches annual precipitation for Redmond weather station, which likely is the lowest annual precipitation in the province.17




According to the 1936 State of Oregon Forest Type Map54 which predates extensive logging activity, about 1% of Mazama Province was then natural grassland, mainly in Klamath and Sycan marshes. About 4% was open and unforested, likely covered by sagebrush and bunchgrasses. About 10% was in stands of western juniper. About 20% was in stands of lodgepole pine, some of which likely represented fire scars. However, some lodgepole stands undoubtedly represented the current ecological stage of succession in forest development. These included stands on imperfectly drained depressions and swales where lodgepole pine is probably the climax tree species because of its tolerance to imperfectly drained situations and cold temperatures.

Most of the province, about 55% of it, was covered by stands of ponderosa pine with some small areas including Douglas-fir and other minor species. About 10% of the province was covered by stands of true fir and hemlock or subalpine vegetation; this was mainly along the top of the Cascade Range. Three isolated areas of true fir–hemlock forest type were mapped on Paulina Peak, Yamsay Mountain, and Gearhart Mountain, each of which is about 8,000 feet or more in elevation.

It is interesting to note pollen analyses that show vegetation on the soils now buried in pumice included many of the tree species still common in the region.14

Mazama Province has the widest range in upland vegetation zones of any of Oregon’s ecological provinces. These zones range from the most arid (10 inches or less precipitation) sagebrush/bunchgrass zone in the northeast of the province to the true fir/hemlock and subalpine zones along the top of the Cascade Range where over 75 inches of precipitation falls annually.

Vegetation zones in Mazama Province are not as closely related to specific soil series or to groups of series as in most other ecological provinces in Oregon. This is largely because soil series in Mazama Province are based primarily on relatively uniform physical characteristics of the overall aeolian pumice mantle. The primary parent material of these soil series is unusually uniform over large areas because of its origin as an aeolian deposit. The result is fewer soil series per given area than when the geomorphology of residual soils is closely related to various landforms and topographic features.

Consequently, a single upland soil series in Mazama Province usually lies in more than one vegetation zone. Conversely, a single vegetation zone may be on more than one soil series. In this situation, the vegetation is much less responsive to the relatively uniform edaphic factors than it is to the prevailing climatic factors or effective environment.



Management Implications

Much of Mazama Province is characterized by a pumice mantle overlying buried landforms, including ancient soils, at depths varying from about 8 to 10 inches up to 40 inches or more. These buried soils, which are usually reddish brown stony to nonstony loams, are important for ecological and management reasons because they lie within the vegetation rooting zone and thereby influence overall soil moisture, nutrient relationships, native species composition and tree growth rates (Fig. 33).

Figure 33: A mantle of aeolian pumice overlying ancient landforms and buried soils typifies Mazama Province in Oregon

The overlying pumice mantle also is important for ecological and management reasons. Individual particles of pumice soil consist of volcanic glass shards which are porous. Consequently, there are more interstices and angles that carry water films— capillary water—than normal in mineral soils of the same texture in which soil particles are solid and rounded. Essentially, porous particles of pumice soil store water within as well as on the surface of each soil particle; solid soil particles in mineral soils store water primarily on the surface of each particle. This beneficially influences the water-holding capacity and cation exchange capacity of the pumice-soil profile.

Furthermore, the mantle of pumice overlying a buried soil apparently acts like a mulch which produces an effective environment more beneficial to vegetation. In the most arid, eastern, portion of Mazama Province this is evidenced by the widespread dominance of Idaho fescue, for example, on pumice-mantle soils. On nearby areas of loamy soils without a pumice mantle, in High Desert Province, Thurber needlegrass and bluebunch wheatgrass are dominant under equivalent climatic conditions. In this particular area, a pumice mantle about 8 to 10 inches thick over buried loamy soil was needed to benefit plants’ effective environment, according to an unpublished field study.32

Another unpublished field study39 made on a tract of Brooks-Scanlon timber land near Bend showed natural regeneration of ponderosa pine on deep pumice sands was very unsatisfactory from a forester’s viewpoint, and junipers encroached following logging. In contrast, at nearby locations where the pumice mantle was about 20 to 30 inches thick over a buried loamy soil, ponderosa pine regeneration was excellent. Furthermore, maturing ponderosa pine trees growing on pumice-loam soils showed significantly better rate of wood production than those growing on nearby deep pumice sands. Obviously, two different ecological situations were involved in this case. The less desirable, from a forestry standpoint, was the ponderosa pine–juniper–bunchgrass vegetation zone, and the more desirable was the ponderosa pine–mixed shrub–bunchgrass zone (Fig. 34). The Brooks-Scanlon forester was much impressed with these soil–plant relationships and that they could be predicted reliably merely by interpreting the ecological indicator species growing on the site.

Figure 34: The ponderosa pine-mixed shrub-bunchgrass zone on pumice-loam soils in Mazama Province, Oregon

At one time, Weyerhaeuser Company at Klamath Falls was having problems with survival of planted ponderosa pine nursery stock on pumice soils. Apparently, this was caused primarily by desiccation due to porous surface layers. Later, an employee solved the problem to a degree by planting nursery stock with 18-inch roots instead of the standard 12 inches.

Examples such as these strongly indicate that the porous nature of pumice particles and, in general, the Mazama pumice mantle, makes it impossible to successfully employ practices and concepts used to manage land and vegetation on conventional mineral soils.

Pumice soils require special knowledge and attention. An unpublished report 30 pointed out that Mazama pumice soils were laid down quite recently, geologically speaking. Weathering and soil formation have not progressed very far. So, now most areas have a surface layer about 12 inches thick, which has undergone weathering and contains incorporated organic matter, underlaid by relatively unweathered pumice.

Although the weathered surface layers’ fertility is usually quite satisfactory, the fresh pumice below is markedly deficient in several nutrient elements, including nitrogen and phorphorus and the minor element boron. The unfavorable nutrient balance may help explain the scarcity of roots in the unweathered pumice.

Pumice soils have unusual moisture relations. Due to its porous nature, pumice soils can retain unusually large quantities of water. However, upward capillary movement of water is slow in these zones. Plant roots must grow down into the moisture. In some areas, on sites that are apparently quite dry, it appears that not all moisture that should be available to plants is utilized. Most of this “surplus” water is contained in the unweathered pumice layers, and it goes unused probably because roots are almost nonexistent in these zones.

Pumice soils are quite easily modified. The changes are noted in characteristics such as bulk density, moisture-holding capacity, capillary movement of soil water, and soil fertility. Compaction resulting from equipment or concentrations of grazing animals considerably modifies pumice soil. This is evidenced by the extremely fine dust common on roads during dry seasons in Mazama Province. Fresh pumice fragments brought to the surface will weather rapidly, much more readily than any other type of volcanic rock.

Dyrness30 emphasized the need to identify and delineate understory plant communities when mapping pumice soils because the presence of a specific group of plants sometimes is indicative of soil characteristics that cannot be easily discerned simply by looking at the soil profile. For example, pumice soil in Mazama Province that is growing snowbrush contains appreciably more nitrogen and calcium than does the soil in bitterbrush areas. Also, grass and forb species in an area may indicate imperfect soil drainage even though soil-profile characteristics may be completely devoid of evidence of a seasonally high water table. This is common on depressions and basins where lodgepole is likely the climax tree species.

Soil survey information alone in areas of immature pumice soils gives an inadequate basis for stratifying land for timber management. This is because young soils tend to exhibit little change in morphological characteristics over large areas even though there may be marked differences in temperature, precipitation, and other important environmental factors. For this reason, surveys in Mazama Province should map both soils and vegetation.


Province Demarcation

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