Willamette Ecological Province

 

 

Location

Willamette Ecological Province in Oregon lies between the Cascade and coast mountain ranges in western Oregon. It extends west to east along the south side of the Columbia River from about Rainier in Columbia County upriver to about Mosier in northwest Wasco County, a distance of roughly 100 riverbank miles. From north to south, it extends from the Columbia River near Rainier to about 25 miles southwest of Roseburg in Douglas County. It is about 50 miles wide, east to west, at Corvallis; the narrowest area, about 15 miles wide, is near Cottage Grove. The province is about 220 air miles long from north to south.

Willamette Province in Oregon covers about 6.2 million acres in Clatsop, Columbia, Tillamook, Washington, Multnomah, Hood River, Yamhill, Clackamas, Polk, Marion, Lincoln, Benton, Linn, Lane, Coos, and Douglas counties. It extends north across the Columbia River into Washington.

 

Description

Physiographically, Willamette Province in Oregon includes nearly the entire drainage system of the Willamette River, which flows into the Columbia River at Portland. It also includes major portions of the Hood River system, which flows into the Columbia River at Hood River, and the Umpqua River system, which flows into the Pacific Ocean at Winchester Bay. To a lesser extent, upper reaches of Nehalem, Siuslaw, and Coquille rivers, which flow into the Pacific Ocean, are within Willamette Province.

Willamette Province has three general geomorphic features:
• Geologically recent alluvial low terraces and floodplains—the valley floor;
• Old valley fill and ancient high terraces; and
• Relatively low-elevation residual hill-lands, mainly less than 1,700 feet elevation, which include the foothills of both the Cascade and coast mountain ranges.

The lowest elevation in the province is about 50 feet at Rainier on the Columbia River. A number of isolated buttes and mountains 2,000 feet or more in elevation are throughout the province. Most of the province is below about 1,700 feet elevation, which is the approximate elevation in the foothills at which western hemlock begins to occur along the Cascade and coast mountain ranges.

Numerous field observations are that the advent of western hemlock in the forest composition is a reliable, widespread ecological indicator of the location on the landscape at which a very significant ecological change occurs in soils, vegetation, and management implications when transecting from arid, warm forest to moist, cold forest. Other species—woody and herbaceous—also change concurrently with the advent of western hemlock.

In Oregon, western hemlock in a forest apparently indicates an effective environment equivalent to 60 or more inches annual precipitation and significantly cooler local climatic conditions.^{34, 35, 36, 37, 44, 45, 46}

Western hemlock, being a tree, reliably indicates average conditions that have prevailed over long climatic cycles. Consequently, western hemlock was chosen as the key indicator species to differentiate Willamette Province, in which western hemlock is not generally common in forested uplands, from the contiguous Cascade and Coast provinces in which western hemlock generally is common in forested uplands.

 

Soils

The geomorphology of soils typifying Willamette Province in Oregon involves a variety of parent materials including geologically recent alluvial low terraces and floodplains in the Willamette Valley, old valley fill, ancient high terraces, and low residual foothills of both the Cascade and Coast mountain ranges. Further complication results from the geographic extent of Willamette Province. The province includes all or part of 16 counties as well as nearly the entire Willamette River drainage system and parts of Hood, Umpqua, Nehalem, Siuslaw, and Coquille rivers’ drainage systems.

Consequently, soil series of Willamette Province are too numerous to categorize. Hhowever, a geographic listing of prominent soil series illustrates how some series are widespread in the province whereas others are more or less localized (Table 43).

 

Climate

Based on 36 official weather stations representing Willamette Province in Oregon, average annual precipitation is about 50.4 inches, of which about 38% falls during the herbaceous-plant growing season, February through June. October through January (winter) precipitation is about 56% of the total. Average January maximum and minimum temperatures are 43.9 and 30.3°F, respectively. Average February through June growing season maximum and minimum temperatures are about 61.4 and 40.2°F, respectively.

The lowest average annual precipitation is recorded at Hood River Experiment Station at 29.5 inches. However, 35% of this falls during the herbaceous-plant growing season, which is typical of the precipitation pattern throughout the province. The highest recorded average annual precipitation is 74.7 inches at the Portland Water Bureau Station on Bull Run River in eastern Clackamas County. Of this, 40% falls during the herbaceous-plant growing season.

Douglas County weather stations are the warmest in the province, undoubtedly because they are near Siskiyou Province to the south, which overall has a warmer, California-type climate.

A precipitation map⁵³ reflects the relatively uniform precipitation pattern throughout Willamette Province in Oregon.

Precipitation and temperature data vary by location, as shown in Table 44.

 

Vegetation

In terms of vegetation, Willamette Province in Oregon is that area below the elevation at which western hemlock grows, starting from the vicinity of Hood River Valley downriver to about Bridal Veil and then south along the foothills of the Cascade Range at about 1,400 to 1,800 feet elevation. The west boundary of Willamette Province is that area below the elevation at which western hemlock grows, from the vicinity of Rainier on the Columbia River south along the foothills and crest of the coast mountain range generally at or below about 1,750 feet elevation. Along both these demarcation lines, Willamette Province is typified by Douglas-fir, white fir, bigleaf maple, and Oregon white oak. By contrast, the Cascade and Coast provinces are typified by the advent of western hemlock in forested plant communities.

Refer to Table 7, in the section on Cascade Ecological Province, for a comparison of the more abundant and characteristic grass, shrub, and tree species in the Cascade, Coast, and Willamette provinces in Oregon.

The southern boundary of Willamette Province is contiguous with Siskiyou Province. Several key indicator vegetation species typify each province. For example, uplands below about 1,300 feet elevation in southern Willamette Province are characterized by common occurrence of bigleaf maple, Oregon white oak, scotchbroom, and small amounts of Pacific madrone. Equivalent uplands in Siskiyou Province are typified by California black oak, wedgeleaf ceanothus, and abundant madrone, which strongly dominates logged and otherwise disturbed forested areas.

Towle³¹ summed up a number of documented observations made in mid-1840s by saying, “The Willamette Valley presented to the first settlers a remarkably open landscape set between the dense forest of the Cascades and the Coast Range. Perhaps Wilke’s [an expedition in 1841] observation that the prairie occupied one-third more of the valley than did woodland is a fair general estimate of its extent.”

Habek¹³ studied land survey records made when Willamette Valley was being subdivided during the 1850s. From survey notes, he constructed a vegetation map that includes seven townships transecting east and west in Marion and Polk counties, a total of 252 square miles. He believed this transect to be representative of a large portion of Willamette Valley at that time. He showed five major vegetational types on the map: oak opening, oak forest, Douglas-fir forest, bottomland forest, and prairie.

Oak openings had trees 50 feet or more apart; if less than 50 feet, they were reported as oak forest. Average distance between trees in oak openings was 143.6 feet compared with 36.5 feet in oak forest. Oak openings were widely distributed in the transect; one township had about 90% oak openings.

Only a small portion of the area included in the transect was covered by oak forest. After valley fires were controlled and oak reproduction was successful in oak openings, the total amount of oak forest gradually increased. Habek¹³ states that in 1961 oak forests were not uncommon in much of Willamette Valley (Fig. 43).

Figure 43: A relict stand of oak forest on the Finley Wildlife Refuge near Corvallis, in Willamette Province, Oregon

Isolated groves surrounded by prairie were limited in species composition to white oak and Douglas-fir with the exception of scattered concentrations of ponderosa pine on more droughty sites, especially in southern parts of the valley.

Habek’s map¹³ shows that Douglas-fir forest dominated both the west and east sides of the valley transect. He noted that this forest type is located at distinctly higher elevations and should perhaps be more properly considered as a part of the mountain ranges on either side of the valley, which is what the concept of Willamette Province does. The high density of trees in the fir forest was one feature particularly noted by early surveyors. Douglas-fir also was locally abundant in ravines and on floodplains.

Bottomland forests occupied the floodplains along creeks and rivers. Four tree species were about equally common: Oregon ash, black cottonwood, Douglas-fir, and bigleaf maple. Other species included white oak, laurel, alder, cherry, and willow. The understory included a large number of shrub species. Towle³¹ calls these bottomland forests “gallery forests.”

Prairie type was grassland vegetation which occupied a rather large portion of mid-Willamette Valley according to Habek’s¹³ map. A small portion was low, wet prairie, and the remainder was upland prairie. Unfortunately, very little information is provided about the kinds of plants that composed the grasslands since surveyors’ references to herbaceous plants were to “grasses,” “ferns,” and “weeds.”

The study made in the Salem area by Nelson²² provides a list of native and introduced grass species. Of the 106 species listed, 55 were introduced species and 51 were thought to be native. That was in 1919. It is interesting that the grasses on well-drained sites include six species of fescue: sixweeks, California, red, western, bearded, and Idaho.

Accurate information about forbs associated with native prairie grasses has not been found. According to Habek, a search for prairie relicts in Willamette Valley was unsuccessful.

According to the 1936 State of Oregon Forest Type map⁵⁴ representing the part of Willamette Province north of Eugene, about 45% of the province was classified as agricultural land. About 35% was classified as forest, including huge areas of heavily cut-over and second-growth trees in Columbia County. About 20% was classified as nonforest. The map, because of scale, does not show the bottomland forests along streams and drainages which, collectively, must have been a significant feature of areas classified as agricultural and nonforest.

In the part of the province south of Eugene, the vegetation pattern was very different due, at least partially, to the narrowing of the valley floor. In this part of the province, about 45% was classified as forest with recent cut-over land around Cottage Grove. About 25% was classified as nonforest, and about 20% was covered by oak.

Authors who have written about Willamette Valley vegetation express little doubt that the potential natural vegetation of the valley and adjacent uplands was a forest system of some type. They also point out that annual fires set by the Calapooya people, and to a lesser extent by early settlers, were probably the single most important barrier to forest expansion.

The scale and frequency of fires declined abruptly with agricultural settlement; this must have allowed woodland to transgress on uncultivated prairie in early days. Areas not cleared for farming likely were transformed into oak forests. As of 1964, an estimated 400,000 hectares (1 million acres) of oak woodland were in the Willamette Valley.²⁹ Open woodland, an extensive type in 1854, had virtually disappeared by 1970.³¹ Level and gently sloping lands, formerly woodlands, were changed to agriculture. On steeper slopes, open woodland changed to forests. The result was a considerable reduction in number of trees in the valley floor and a considerable increase in the number of trees in the hills.

Several other authors have published assessments of Willamette Province vegetation from a historical viewpoint.^{10, 16, 25, 27}

The data for Lane County represent a reasonable cross-section of Willamette Province climatic conditions. The county lies in the center of the province, and data include three stations on the main valley floor and three stations in extensions of the valley eastward up major drainages.

It should be noted that the three weather stations in Douglas County, which reflect average January temperatures that permit growth of herbaceous plants all winter, are in the Umpqua Valley. This is at the south end of Willamette Province, contiguous to Siskiyou Province, where a California-type climate prevails.

 

Management Implications

In managing Willamette Province’s natural resources, it is essential to recognize that the basic ecology has not changed over time. Unless humans intervene, the trend still is and will continue to be some sort of plant succession toward a forest climax type because of climatic factors in Willamette Province that favor tree growth.

Calapooya people managed the resources for their use with annual fires. Early settlers also used fire but to a lesser extent. As human activities increased and expanded in the province, more and more restrictions on using fire have been enforced. Consequently, prescribed fire is virtually always against some law, except for limited and specifically approved field and slash burning. Essentially, this means that the natural ecological succession in Willamette Province is largely unimpeded except where farming practices and approved chemicals, or housing developments, are applicable (Fig. 44).

Figure 44: Agriculture in close proximity to woodland is common in Willamette Province, Oregon

In the absence of fire, weeds and brush are early successional stages in a forest climax type. On permanent pasture, grazing alone is not likely to control brush encroachment permanently. Severe utilization of the pasture may actually accelerate brush encroachment and, eventually, tree encroachment. However, using selected classes of animals, such as sheep and goats, and beneficial grazing management may be reasonably successful in postponing natural ecological succession toward a forest climax type.

Encroachment and increased density of woody species in Willamette Province, which naturally occurs in successional stages toward forest climax, should be expected unless deliberately controlled. Increasing forested areas, coupled with growing demand for housing sites in a perceived rural lifestyle, increases the risk of wildfire damage; increases public costs for transportation, sewage, domestic potable water, pollution control, household services, roads, and police protection; and sets up conflicts between residents and those who work in agriculture and forestry, even when these enterprises are in equilibrium with sustainable uses of a healthy forest climax.

As population increases in Willamette Province, social aspects of managing natural renewable resources in the province certainly are going to increase in prominence unless action is taken to protect and maintain the natural heritage and its sustainable uses.

 

Province Demarcation

Willamette and Coast Demarcation

Starting just west of Rainier on the bank of Columbia River in Columbia County, the line of demarcation between Willamette and Coast provinces in Oregon goes west atop steep slopes overlooking Columbia River 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 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 travels 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 and crosses 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 winds southeast at about 1,750 feet elevation to the Tillamook–Washington county line. It turns 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 run south around the headwaters of drainages flowing eastward into Tualatin and North Yamhill rivers.

Northwest of McMinnville, the line makes a huge swing westward at about 1,750 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 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 southwest Polk County, the line descends the ridge southeasterly to cross Luckiamute River at about 650 feet elevation. It climbs Cougar Ridge and then winds south along the crest of the Coast Range. The Coast Range drops in elevation on the narrow divide between Marys River and Yaquina River to about 730 feet elevation at the community of Summit, about 5 miles northwest of Blodgett on Highway 20.

From the community of Summit, the 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 goes south along the crest of the Coast Range to Marys Peak, winding north and east around Mary’s Peak at about 1,700 feet elevation. The line crosses the pass on Alsea Highway (Oregon 34) at about 1,125 feet elevation, runs southeast up the ridge and around the east slopes of Flat Mountain at about 1,750 feet elevation, and continues south at about that 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 line of demarcation between Willamette and Coast provinces 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 to wind southeasterly along the crest of the Coast Range, 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 river crossing, 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 Coast Province, which is typified by the occasional Sitka spruce tree. From the vicinity of King Ranch on the Siuslaw, the line travels southerly along the divide between Siuslaw and Smith rivers and then westerly 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 turns south to cross Umpqua River at Scottsburg community.^{36, 91} 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 from drainages flowing to the west into Coos and Coquille rivers.

The demarcation line crosses the Coos Bay Wagon Road west of Reston community, which is in Willamette Province, at 1,850 feet elevation and continues southwest at about 2,000 feet elevation.^{36, 91}

About 7 miles southwest of Camas Valley community, in Willamette Province, the line of demarcation 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 It is near the southeast end of Chipmunk Ridge that Willamette, Coast, and Siskiyou provinces join.

The line of demarcation between Willamette and Coast provinces is based primarily on the elevation at which western hemlock grows. However, the line also is indicated by the general presence of such forested soils as Bellpine, Jory, Retner, and Bateman series, which typify Willamette Province, and Bohannon, Blachly, Preacher, and Digger series, which typify Coast Province.

Although the line of demarcation is based on the elevation at which western hemlock generally is common in forested uplands, it is interesting to note that at locations along the Coast Range crest where 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 Nehalem River drainage, the province line is about 1,600 feet elevation. The Gales Creek Highway (Oregon 6) summit into Wilson River drainage also 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 Willamette–Coast 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 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 between Willamette and Coast provinces apparently represents where the effects of the warmer, drier Willamette Valley climate are overcome by the more moist, cool coastal climate.

Willamette and Siskiyou Demarcation

From the junction of Willamette, Coast, and Siskiyou provinces near Chipmunk Ridge in southwest Douglas County, the line of demarcation between Willamette and Siskiyou provinces goes along the ridgetop north to the vicinity of Live Oak Mountain and continues northerly to circle the headwaters of Olalla Creek, which are in Siskiyou Province, and then south to Table Mountain. From there, the line meanders northeasterly along the ridgetop past Buck Mountain at about 2,500 feet elevation. About 4 miles northwest of Riddle, in Siskiyou Province, the line veers north and northwest by Big Baldy Mountain along the ridge separating drainages flowing west into lower Olalla Creek, in Willamette Province, from drainages in Siskiyou Province that are flowing north.

The line descends northwesterly to the edge of bottomlands along Olalla Creek at about 600 feet elevation and follows the southern border of these bottomlands north and east and along South Umpqua River, which is in Willamette Province at this location, to the bridge where Highway I-5 crosses South Umpqua River.^{36, 95}

From the I-5 bridge across South Umpqua River, the line climbs the ridge northeast to Dodson Butte, Brushy Butte, and Lane Mountain. It is near Lane Mountain that the Willamette, Siskiyou, and Cascade provinces join.^{36, 51}

The line of demarcation between Willamette and Siskiyou provinces, which is about 70 miles long, is not clear-cut in terms of soil or vegetation differences throughout its extent. Both provinces have arid, warm climates with Siskiyou being relatively more arid and warm than Willamette Province. The line was judged using data in the 1993 Preliminary General Soil Map, Douglas County, Oregon,⁹⁵ which covers the area where the 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 presence 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. Certain segments of the demarcation line between Willamette and Siskiyou provinces demonstrate these vegetation comparisons.

Willamette and Cascade Demarcation

From the junction of Willamette, Siskiyou, and Cascade provinces near Lane Mountain about 10 miles east of Roseburg, the line of demarcation between Willamette and Cascade provinces goes north at about 1,500 feet elevation on north-facing slopes and at about 2,800 feet elevation on west- and south-facing slopes. The line is based on the advent of western hemlock in the forest which signifies the colder, more moist effective environment of Cascade Province as compared with Willamette Province.

The line travels east around the upper reaches of drainages into Little River and then northwest at about 2,000 feet elevation in the vicinity of Shivigny Mountain, which is in Cascade Province. It continues on northwesterly to cross North 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 heads north at about 2,000 feet elevation around the west slopes of Scott Mountain, Brown Mountain, and across Calapooya Divide. From near Calapooya Divide, the line goes north at about 1,800 feet elevation to the vicinity of Cottage Grove, extending up each major drainage that flows into Coast Fork Willamette River.

Northeast of Cottage Grove, which is in Willamette Province, the line goes generally north at about 1,800 feet elevation but extending up each major drainage that flows into Willamette River from the east. The line extends up Middle Fork Willamette River to about 17 miles south of Oakridge, which is in Willamette Province. The line extends up McKenzie River to near Belknap Springs; up Calapooia River to about King Camp; up South Umpqua River to about House Rock Forest Camp; up Middle Santiam River to just below Green Peter Dam; up North Santiam River to about 6 miles east of Mill City; up Little North Santiam River to about Elkhorn; up Clackamas River to about Fish Creek; and up Sandy River to about Brightwood.

The pattern of western hemlock growth, extending east up each major drainage that heads in the Cascade Mountains, signifies the effects of the warmer, drier Willamette climate extending up these valleys.

The line between Willamette and Cascade provinces near Firwood on Highway 26 in Clackamas County is at about 1,600 feet elevation. Farther north along Sandy River southeast of Portland, western hemlock occurs at about 1,400 feet elevation, including near Bridal Veil on the Columbia River. From the vicinity of Bridal Veil, the line of demarcation winds easterly along steep breaks of Columbia Gorge to pass west and south of Hood River Valley, which is in Willamette Province, at about 3,000 feet elevation. It continues to a point about 6 miles south of Parkdale in upper Hood River Valley. Near here, Willamette, Cascade, and The Dalles provinces join.

Although the line of demarcation between Willamette and Cascade provinces in Oregon is based primarily on the elevation at which western hemlock grows, the line also is indicated by the general occurrence of such forested soils as Honeygrove, Peavine, Bellpine, Philomath, Jory, Cazadero, Parkdale, Hoodview, and Bins, which typify Willamette Province, and by Klickitat, Kinney, Bohannon, Holderman, Henline, Aschoff, Bull Run, Divers, and Thader, which typify Cascade Province.

Willamette and The Dalles Demarcation

From the junction of Willamette, Cascade, and The Dalles provinces in Oregon, the line of demaracation between Willamette and The Dalles provinces runs along the ridge east of Hood River Valley and northeast down the ridge nearly to Highway I-84 along the Columbia River. Here it veers sharply upriver nearly to Mosier, which is in The Dalles Province. The towns of Hood River and Parkdale and the entire Hood River Valley are in Willamette Province; this is substantiated by the common presence of bigleaf maple, which does not grow in The Dalles Province.

The line between The Dalles and Willamette provinces in Oregon, which is about 30 miles long, is based on soil lines between Hood, Van Horn, Oak Grove, and Bins series, which typify Willamette Province in the vicinity of Hood River Valley, and Bald, Bodell, Frailey, and Ketchly series, which typify The Dalles Province in Oregon.⁸⁹