Snake River Ecological Province

 

 

 
 
 

Location

This province in Oregon includes the western portion of the huge Snake River basin that extends east across southern Idaho. In Oregon, the province covers about 4.9 million acres, mainly in Malheur and Baker counties but with small segments in Harney, Grant, and Union counties. It extends eastward into Idaho.

 
 

Description

Snake River Province of Oregon is typified by extensive dissected terraces formed in ancient lakes. These terraces are geologically eroded to the point that they appear as plateaus, basins, low rolling hills, and prominent hills separated by sharp dendritic drainage patterns. Mountainous terrain is interspersed throughout most of the province (Fig. 39). For example, Lookout Mountain is basaltic/granitic; the mountains south of Burnt River are largely limestone from which cement is ground from open-pit mines at Lime; and other mountains, such as Ironside Mountain, Cedar Mountains, and Owyhee Ridge just east of Owyhee Reservoir, are rugged basaltic formations.

Figure 39: Dissected ancient-lake terraces, hills and interspersed valleys characterize Snake River Province, Oregon

Alluvial valleys, which are used for irrigated agriculture, run along major watercourses. These include Eagle Valley, Keating Valley, Baker Valley, North Powder Valley, Burnt River Valley, and the extensive valley around Vale, Ontario, and Nyssa. Some low-lying terraces are irrigated in the Vale–Ontario vicinity, near North Powder, around the north and west perimeter of Baker Valley and in Eagle Valley.

Elevations within Snake River Province are mostly between 3,000 and 5,000 feet. The lowest point, about 1,800 feet, is at Copperfield on the Oxbow of Snake River where it exits this province and enters Blue Mountain Province to the north in upper Hells Canyon. High promontories within Snake River Province include Mahogany Mountain at 6,524 feet, about 14 miles northeast of Sheaville in Malheur County; Bald Mountain at 6,683 feet, about 15 miles south of Baker City in Baker County; Castle Rock at 6,847 feet, about 8 miles north of Beulah in Malheur County; Lookout Mountain at 7,127 feet, about 12 miles south of Richland in Baker County and only about 35 air miles from the lowest point on Oxbow; and Ironside Mountain at 7,815 feet, about 12 miles southwest from Ironside in Malheur County.

 
 

Soils

The soils formed on ancient terraces in Snake River Province vary considerably by location according to the terrace materials in which they were formed. Some are very gravelly, some are stony, some are nonstony. Most of these terrace soils have medium- to fine-texture surface layers and clayey subsoils. Depths vary from shallow to deep, and soils may be underlain by hardpans. A good example of ancient-terrace soils underlain by hardpans can be studied on Highway 86 roadcuts in the vicinity of Virtue Flat about 12 miles east of Baker City.

Soils formed on mountain slopes may be shallow to deep, nonstony to very stony. They usually have medium-texture surface layers and clayey subsoils.

Soils in valleys are usually deep, of medium texture, moderately well drained, and fertile. Some bottomlands, however, are imperfectly to poorly drained, usually moderately deep over hardpans, and are alkaline or sodic.

 
 

Climate

For nine of the 14 official weather stations, which represent a cross-section of the province, the average annual precipitation is about 9.9 inches, of which only 28% occurs during the native-plant growing season, April through June. November through March precipitation is about 55% of total annual precipitation. Average January maximum and minimum temperatures are 35.5 and 16°F, respectively. Average April through June maximum and minimum temperatures are 71.3 and 39.6°F, respectively.

Precipitation and temperatures vary by locality, as shown in Table 37.17

Field observations in Snake River Province indicate the existence of storm patterns which appear to be related to the mountainous topographic features that help typify this province. Consequently, paths followed by these storms receive considerably more precipitation than other areas just a short distance away, but this is not documented by existing official weather stations. However, both soils and plant communities reflect these favorable moisture conditions which are highly significant from a resource management aspect, especially when they occur during the native-plant growing season.

A precipitation map53 shows greater than 15 inches precipitation for mountainous areas in the province and about 30 inches precipitation for the Lookout Mountain– Sheep Mountain–Little Lookout Mountain group southeast of Baker City, which is the highest precipitation shown for the province.

 

 
 

Vegetation

According to the 1936 State of Oregon Forest Type Map, 54 which predates extensive logging, only about 0.4% of Snake River Province was covered by coniferous trees at that time.

About 0.1%, or 66,000 acres, was covered by stands of western juniper which grew primarily in five general locations. About 23,000 acres were in the extreme southwest part of the province on mountainous terrain. About the same acreage was in the area between Juntura and north to the vicinity of Beulah Reservoir. North of the Burnt River in the vicinity of Hereford about 7,000 acres of juniper grew on upper portions of south-facing slopes. Also along Burnt River about halfway between Bridgeport and Durkee, about 6,000 acres were near ridgetops on south-facing slopes. On the south-facing slopes of Lookout Mountain were stands of juniper totalling about 7,000 acres.

Ponderosa pine, primarily stands of large old-growth, was on about 134,000 acres or 0.3% of the province. Some of these stands were along the line of demarcation between Snake River and Blue Mountain provinces; the largest area of about 46,000 acres was from Whitney southward. Other stands of ponderosa pine grew in the interior of the province. The east–west ridge between Burnt River and Powder River had about 80,000 acres of pine. This stand includes the Dooley Mountain area. In the high country southwest of Bridgeport between Burnt River and the headwaters of Willow Creek were stands covering about 6,000 acres. In Timber Canyon on the north-facing portion of Little Sheep Mountain were about 1,000 acres of pine and Douglas-fir. And, a small stand of pine and Douglas-fir appeared on the north-facing slopes of Lookout Mountain.

In terms of acreage, the vegetation of Snake River Province is primarily a shrub–grassland climax type. Sagebrushes dominate the aspect; however, the province is characterized by a variety of shrub species that flourish on the hills and terraces above the most arid low-lying portions of the province (Fig. 40).

Figure 40: A managed shrub-grassland range in Snake River Province, Oregon

Wyoming and basin big sagebrushes are the most prominent shrubs on uplands. Basin big sagebrush also grows on well-drained bottomlands. Greasewood and green rabbitbrush are typical of sodic bottomland sites. Mountain big sagebrush appears in higher elevations where precipitation is about 12 inches or more. Rigid and threetip sagebrushes grow mainly on shallow clayey scabland sites. Louisiana wormwood grows on some moist bottomland sites. Bitterbrush, squawapple, currants, chokecherry, buckwheats, gray and green rabbitbrushes, gray horsebrush, and spiny hopsage are on various rangeland sites. Curlleaf mountain-mahogany occurs on rocky outcrops and ridges.

The basic perennial grasses on rangeland sites in the province are bluebunch wheatgrass, Idaho fescue, Sandberg bluegrass and squirreltail. Indian ricegrass, Thurber needlegrass, and needle-and-thread also grow on the more arid sites. Onespike oatgrass, Kentucky bluegrass, Columbia and western needlegrasses, and oniongrass also grow in more moist upland sites. Basin wildrye is common throughout the province on concave areas or those with deeper soil in the uplands as well as on nearly all bottomland sites and riparian areas that have not been farmed. Cheatgrass is very prolific throughout the province. Medusahead wildrye signifies clay spots. Beardless bluebunch wheatgrass grows in the Baker County portion of the province.

Over 100 species of perennial forbs have been recorded as regularly growing on upland sites in this province. This obviously is an incomplete record. Even the most arid sites in this province are characterized by a good variety of 25 or more perennial forb species.

Forested areas in the province are on higher elevations and north-facing slopes in mountainous areas. They consist mainly of combinations of ponderosa pine, Douglas-fir, and grand fir with some western juniper on shallow rocky areas and in the fringe between timbered and sagebrush areas. Shrubs commonly associated with forested areas include wax currant, low Oregon-grape, rose, serviceberry, and spirea. Grasses include Idaho fescue, bluebunch wheatgrass, elk and threadleaf sedges, Kentucky, Canby, and Sandberg bluegrasses, prairie junegrass, Columbia needlegrass, pinegrass, and basin wildrye. A wide variety of shade-tolerant forbs grow in this coniferous tree climax type.

Originally, basin wildrye probably dominated most, if not all, bottomlands and riparian areas in the province, whether moist, semimoist, alkaline, or otherwise. Associated grass, forb, and shrub species varied according to degree of wetness and alkalinity.

 

 
 

Management Implications

The province includes irrigated intensive agriculture in the Vale–Ontario–Nyssa area which is devoted primarily to growing food for human use. All other valleys in the province are essentially fully used for irrigated agriculture with emphasis on production of livestock forage and feeds.

A large proportion of the province is public land, especially in Malheur County which is about 80% public land. The Baker County part of the province has a much lower proportion: about 40% publicly owned lands. Management of the public lands indirectly exerts a significant influence on the use and management of private lands in the province. Resource issues, problems, opportunities, and options nearly always involve both kinds of ownerships in the province, especially in the northern portion. This makes the coordinated resource management planning (CRMP) process a very appropriate way to resolve issues and improve overall resource management.

Some rangelands in the low-precipitation areas near Snake River have been irretrievably damaged by nearly a century of excessive livestock grazing, wildfires, soil erosion, and possibly dryland farming. The result has been significant changes in soils and their capability to recover naturally within an acceptable time. Seeding to selected forage species, together with prescribed grazing systems, have proved successful in returning these lands to forage production as well as in much improving watershed quality and wildlife habitat.

In areas of about 12 inches precipitation or more, the soils inherently are more able to recover from past uses. This has been demonstrated on many ranches in the province where modern range management technology has installed practical grazing programs with good success. Although the nature of the terrace soils is such that erosion and compaction are serious considerations, these soils also respond well to seeding for rehabilitation.

The BLM Vale Project covered a large portion of the province in Malheur County, and other programs promoted by the Vale BLM District treated much BLM land in Baker County. Consequently, many effective rangeland manipulations and improvements have been made. This benefitted many resource values including wildlife habitat, recreation, watershed quality, and range condition in addition to providing great benefits to livestock ranching. There are many examples of treatments that are effective, and some that are not, for the soil, topographic, and climatic conditions on both public and private lands in the province.

From the viewpoint of watershed quality and soil erosion, which are most important considerations, it is highly desirable to culturally revegetate all suitable soil areas in the province that are seriously depleted and not likely to recover naturally because of permanent changes in the original soil situation and plant cover. Delays in revegetation run the risk of soil erosion, leading to a new, lower potential state. In the long run, for the health and stability of the basic resource—soil—it is far more judicious to revegetate these areas by seeding as soon as possible.

 
 

Province Demarcation

Snake River and Blue Mountain Demarcation

The line of demarcation between Snake River and Blue Mountain provinces in the northeast begins in the Snake River canyon at Copperfield on the Oxbow where the river exits Snake River Province and enters Blue Mountain Province in upper Hells Canyon. From that point, the line runs southwest up the ridge between Pine Creek and Snake River. All drainage into Pine Valley and Pine Creek is considered to be in Blue Mountain Province, although the deep Snake River canyon makes this line a matter of judgment based mainly on native plant communities and soils. All of Eagle Valley is in Snake River Province. From the divide on Highway 86 between Eagle Valley and Pine Valley, the line runs westerly at about 4,000 feet elevation along the upper edge of the ancient terraces south of Sparta. In this area between Eagle Valley and Keating Valley and north of Powder River, there are excellent examples of dissected ancient terraces which typify Snake River Province (Fig. 41).

Figure 41: Prominent ancient-lake dissected terraces north of the Powder River in easter Baker County represent the northern boundary of Snake River Province in Oregon where it butts into the mountainous Blue Mountain Province (background) at about 4,000 feet elevation.

The line of demaracation crosses into Union County east of Pondosa at about 4,000 feet elevation and continues northwesterly through Telocaset and around the north and west edges of North Powder Valley, then south at about 4,000 feet elevation to just west of Baker City. There, an apparent geological uplift has abruptly placed the upper line of the terrace at about 4,500 feet elevation. The line continues south at about 4,500 feet elevation until just west of Unity where another apparent uplift places the upper terrace level at about 5,000 feet elevation.

The demarcation line ends southwest of Ironside Mountain where Blue Mountain Province reaches its most southern point and joins John Day Province to the south. Ironside Mountain is in Snake River; Strawberry Mountain and Prairie Hill are in Blue Mountain; Antelope Mountain east of Seneca is in John Day Province.

Snake River and John Day Demarcation

The line of demarcation between Snake River and John Day province to the west, which is about 5,000 feet elevation on the uplifted area east and south of Antelope Mountain, drops down to about 4,500 feet west of Drewsey and Warm Springs Reservoir and proceeds south along the east slopes of Stinking Water Mountains.

Snake River and High Desert Demarcation

Just east of Crane, the line of demarcation between Snake River and High Desert provinces begins at about 4,250 feet elevation. It is at this point, the gap at Crane, that one might speculate about how the ancient lake, in which the terraces of Snake River Province were formed, at one time might have been connected to the ancient lake in which the terraces of the High Desert Province were formed. For this to have happened, the lakes would have had to exist simultaneously. But this is a matter of conjectural paleontology and has no current significance in differentiating between the two provinces. Obviously, the terraces and basins in High Desert Province suggest quiet-water abatement which seems logical for such interior basins that had no strong currents escaping to the ocean. In contrast, the terraces of Snake River Province are typified by strong geologic erosion and sharp dendritic drainage patterns which suggest that the water receded in strong currents out through Snake River to the ocean. Consequently, the kinds of ecological sites (soils, plant communities, topography) and especially the management implications are markedly different between Snake River and High Desert provinces.

Demarcation between the provinces is likely a belt south and east of Crane to the vicinity of Folly Farm and northeast toward Crowley. There is no readily apparent line of demarcation anywhere within this belt; therefore, the line becomes a matter of field experience and judgment. Based on the fact that ancient-terrace lines are extensive and consistently visible at about 4,500 feet elevation around the perimeter of the geologic basin that forms High Desert Province, and that the Snake River Province line west of Warm Springs Reservoir is at about 4,500 feet elevation, the line of demarcation between Snake River and High Desert provinces has been placed at about 4,500 feet elevation from the vicinity of Crane southeast to just north of Folly Farm, then northeast to just north of Crowley. From there it runs east around the south side of Cedar Mountains to the rim of the Owyhee River canyon, which is at 4,000 feet elevation. This line places the dry lakebeds and closed basins south of Crowley in High Desert Province, which is typified by similar closed-basin topography, whereas Snake River Province to the north is typified by landscape dissected by dendritic drainages into the Snake River system.

Snake River, Humboldt, and Owyhee Demarcation

Snake River Province includes the Owyhee River canyon up to about 6 miles upstream from Rome. In this canyon are exposed thick layers of sedimentary or tuffaceous materials that typify Snake River Province. The basalt plateau and terraces to the west of the canyon are in Humboldt Province; those to the east of the canyon are in Owyhee Province.

From the vicinity of Rome and Arock, the line between Snake River and Owyhee provinces goes north along the rim of Owyhee River canyon at about 4,000 feet elevation. It follows this elevation, which is the approximate break between the higher basalt plateaus and hills of Owyhee Province and the exposed sedimentary materials lying to the north at lower elevations, which typify Snake River Province. The line of demarcation follows along the north side of Mahogany Mountains east to Rockville and then north and east into Idaho at about the 4,000 foot elevation.