Great Basin Shrub-Steppe, North Portion, Part I

Montane Forests and the Cultural Landscape of the Desert
Ice Age Lakes, Historic Trails, and Nevada’s Yosemite
I. Map Focus Area: 40 to 43 degrees North, 111 to 121 degrees West
II. Countries and Subdivisions (States): United States (California, Idaho, Oregon, Utah)
III. Overview
The most important event influencing the northeastern Great Basin in the map area was the prehistoric presence of Lake Bonneville and Lake Lahontan. Lake Bonneville occupied the eastern portion, and Great Salt Lake is its remnant. Lake Lahontan occupied the western portion, and the Humboldt River and Carson River sink (south of the map area) is its remnant. At about 15,000 years Before Present (BP), Lake Bonneville reached its highstand of 1552 m elevation and was a trout-filled cold water body. The fluctuations of the lake influenced much of the area. During the highstand, Lake Bonneville overflowed to the north into the Snake River basin. However, at 14,500 BP, an alluvial dam at Zenda, Idaho (site 1 on map, south of Downey on US 91), collapsed, producing a massive flood. The peak discharge into the Snake River, one million cubic feet per second, was the equivalent of all the world’s rivers combined. Within a year the lake stabilized at 1,444 m when the water erosive force met bedrock at Red Rock Pass, Idaho, near Downey on US 91. However, increasing aridity caused the lake to continue to decline in elevation to where it reached the current level of Great Salt Lake by 11,300 BP. This level was accompanied by a massive die-off of fresh water fish. There have been other fluctuations, but the lake has always returned back to Great Salt Lake levels (Rhode et al. 2005).
For emigrants to California in the 1840s and 1850s, perhaps the most arduous portion of the trip was across the Great Basin desert of northern Utah and Nevada. Today a number of sites commemorate the historic trails; many are on public land and can be visited. A more detailed listing is described under the California National Historic Trail entry. The Pony Express also crossed the Great Basin desert, as did the transcontinental railroad. Both are commemorated by remnants which can be visited. In 1846, California-bound immigrants known as the Reed-Donner party left the established California Trail at Fort Bridger, Wyoming and attempted the Hastings Cutoff. The Donner party encountered a two-week delay in the Wasatch Mountains and was already very late in the year when they entered today’s Nevada to the west of the Great Salt Lake. On the first week of October, they arrived at a sharp bend in the Humboldt River known today as Iron Point (site 2). It was most expedient at that point to drive the oxen up a steep hill which provided a shortcut and connected back with the river valley. The last of the party to attempt the hill were wagons driven by John Snyder and Milford Elliott, driving the wagon of James Reed. When their cattle became entangled, the men started to quarrel, which led to the stabbing death of Snyder by Reed (Grebenkemper, Johnson, and Morris 2012).
The Great Basin shrub-steppe ecoregion in Utah and Nevada extends from Great Salt Lake in the east to the Sierra in the west. Habitats in Utah are dominated by barren salt deserts containing playas, salt flats, mud flats, and saline lakes. Around the perimeters of the salt deserts are shadscale-greasewood areas. Mountainous areas south of Great Salt Lake support woodlands with forests in the highest elevations. There are wetter areas draining the west side of the Wasatch Mountains, and this is where the population centers such as Salt Lake City are located. Extensive areas of wetlands adjoin the eastern Great Salt Lake. Habitats in eastern Nevada are many of the same as in Utah, but as the land continues west into the Humboldt River drainage things get even hotter and drier. Marshes, remnant lakes, and playas remain from the Pleistocene-age Lake Lahontan. Other portions of the former lakebed are dominated by salt-tolerant shrubs. Sagebrush is on the slopes and low mountains. Uplands in the Lahontan area support grasses and pinyon-juniper vegetation.
The Great Basin shrub-steppe ecoregion includes a portion of southeastern Idaho south of the Snake River. In this area the Great Basin is a high plateau overlooking the Snake River plain. The Idaho areas are less arid than the portions of the Great Basin in Nevada and Utah and tend to be dominated by sagebrush grassland at lower elevations, with mountain big sagebrush, small areas of juniper and woodland of aspen, Douglas-fir, and lodgepole pine at higher elevations. The Idaho portions tend to be less arid than the Snake River Plain to the north. The mountains tend to have more woodland than the rest of the Great Basin, and a number of areas have been designated as national forests. The perennial water source in the Great Basin in this area is the Bear River, which flows north through the Wyoming shrub-steppe into Idaho. Originally, the Bear River flowed northward to the Snake. However, about 140,000 years ago lava flows north of Soda Springs (site 3) blocked the water and it diverted south to the Great Salt Lake.
One of the most infamous environmental incidents in the Great Basin occurred in 1968 at Skull Valley, Utah (site 4). As described in Science at the time, “nine months ago, some 6,000 sheep grazing in Skull Valley, Utah, were killed or sickened by a mysterious ailment that attacked the central nervous system.” The agent proved to be VX, a type of nerve gas that was apparently being tested just to the west at Dugway Proving Grounds. The sheep likely ingested the nerve agent by eating contaminated vegetation. A Utah senator disclosed that nerve agents had been used in the area at the time the sheep were killed (Boffey 1968). There were concerns that such open-air testing could lead to adverse human health effects. The timing of the incident and accompanying outrage added fuel to the birth of the environmental movement.
Another incident in environmental history in the Great Basin also occurred during the 1960s. There were plans to raise the height of American Falls dam to store more irrigation water. However, the higher water would flood the Fort Hall bottoms and the project was opposed by the Shoshone-Bannock Tribe, which controlled the south side of the bottoms (Nelson 1968). The dam was reconstructed with the same pool.