Great Rift of Idaho, Megafloods Natural and Manmade and on Mars, Niagara of the West, Thousands of Springs
States: Idaho and Wyoming
Coordinates: 42 to 45 degrees North, 111 to 115 degrees West
There are several distinct areas of the shrub-steppe ecoregion of the Columbia Plateau. For the purposes of this discussion, the Snake-Columbia shrub-steppe ecoregion is subdivided into four sections, based on biological or geographic criteria. These are the Upper Snake River Plain, Treasure Valley and Owyhee Uplands, Oregon Lakes, and Columbia River Scablands.
The first area is the Upper Snake River Plain of southeastern Idaho and about a mile of Wyoming, which begins at the Magic Valley and extends east to the Wyoming border. Shoshone Falls within the Magic Valley is a biogeographic boundary, separating aquatic fauna upstream from downstream. The Magic Valley is an area of irrigated cropland which includes the lower Wood River, Thousand Springs Area, and Twin Falls upstream to Minidoka Dam. From American Falls upstream to St. Anthony is another agricultural area, the Upper Snake River Plain. The Teton Basin along the Teton River upstream from Rexburg is also an agricultural area. The area north of the Snake River is sagebrush and bunchgrass and is used for rangeland. Scattered lava flows and other volcanic features are present at Craters of the Moon National Monument and Preserve and Hells Half Acre. The three dry intermontane valleys drained by the upper Salmon River, Pahsimeroi River, Lemhi River, Birch Creek, Big Lost River, and Little Lost River are also sagebrush-covered and included in the ecoregion.
The entire Upper Snake River Plain contains lava flows created by the Yellowstone hotspot. The area was also shaped by megafloods. The notable Lake Bonneville dam failure and drainage about 15,000 years ago is believed to be responsible for some of the deep gorges along the Snake River. The spectacular Shoshone Falls (1), nicknamed as the Niagara of the West, is located in a city park in Twin Falls, which is part of the Magic Valley. Other tributary streams entering the Magic Valley also cut deep gorges. Downstream of Shoshone Falls the canyon walls are notable for seepage, creating the Thousand Springs area. Some canyons in the Thousand Springs area, such as Earl M. Hardy Box Canyon Preserve in Thousand Springs State Park (2), N42˚42’ W114˚49’ and adjacent Blind Canyon, have no drainage network upstream, and seepage emanates from the headwall. This type of feature has long been interpreted by geologists as resulting from seepage over thousands of years. At Box Canyon, the 11th largest spring in the United States creates a stream that flows a couple of miles into the Snake River. Lamb et al. (2008) reported that the head of the canyon actually contains waterfall plunge pools, and that there was evidence of past overspill in a large waterfall. The scour is not visible upstream because loess has been deposited on top of it. The age of the scoured bedrock notch at the head of the canyon was estimated at 45,000 years Before Present. This flood took place before the Bonneville event. The water source was probably the Big Lost River drainage or the Big Wood River drainage. Both rivers had megafloods when glacial lakes burst during the Pleistocene. These canyons are similar in appearance to many Martian canyons, and these are thus believed to be useful analogs to how the Martian canyons formed (Lamb et al. 2008).
Humans accidentally produced a smaller-scale megaflood of their own in 1976, when the Teton Dam collapsed while the reservoir was filling. Teton Dam (3), N43˚55’ W111˚32’, was located upstream from Rexburg in on the Teton River. Construction on a dam which would create a 17-mile-long reservoir commenced in 1975. The collapse of the partly filled reservoir in June 1976 caused extensive flooding downstream and damaged the hydroelectric facilities at Idaho Falls. The collapse occurred when the reservoir was only 22 feet before reaching full pool and was 270 feet deep. In about six hours, 250,000 acre-feet of water drained from the reservoir. The death toll downstream was 14. The government eventually paid about $400 million in damages to downstream users, including $1.7 million to the Idaho Department of Fish and Game for natural resource damages (Randle et al. 2000).
Initial investigations into the Teton Dam collapse focused on concerns about earthquake faults in the dam vicinity, raised in memos by the US Geological Survey (Boffey 1976). However, the December 1976 official report of an independent group blamed the dam collapse on poor engineering design work. The panel found evidence that water from the reservoir traveled through fissures in the canyon wall and made its way to the dam where it created tunnels and weakened the structure. Although the Bureau of Reclamation grouted the fissures and had built 250 earlier earthfill dams with no failures, geological conditions at the site were unusual and probably warranted additional measures (Boffey 1977). The dam was never reconstructed.
There is one Western Hemisphere Shorebird Reserve Network site in the Upper Snake River subsection, American Falls Reservoir/Springfield Bottoms, Bureau of Reclamation, Idaho (4); coordinates are N42˚51’ W112˚50’. At 56,000 acres, this is one of the largest irrigation reservoirs, storing 1.7 million acre-feet of water as part of the Minidoka Project. A visitor center is at the dam, and a fish hatchery with nature trail along the Snake River (Idaho Department of Fish and Game) is below the dam. The reservoir is an Important Bird Area (IBA) for the California gull and waterbirds. Fort Hall National Historic Landmark (described below) is at the upper end on the Snake River opposite McTucker Island. The Fort Hall (Springfield) Bottoms are a waterfowl feeding ground fed by up to 50 cool, clear springs. The Sterling Wildlife Management Area on the reservoir is 3,600 acres covering a seven-mile stretch of the northern shoreline. It contains 1,500 acres of wetlands and is itself an IBA for waterbirds and shorebirds.
There are three National Historic Landmarks in Upper Snake River Plain. Two of them, Fort Hall and the Camas Meadows Battles, commemorate frontier history. Fort Hall, American Falls Reservoir and Fort Hall Indian Reservation (Shoshone-Bannock Tribe), Idaho (5) , N43˚1’ W112˚38’, was a fur trade outpost dating to 1834. It became the most important trading post in the Snake River Valley, established by Americans in disputed territory. It was also associated with overland migration as a stop on the Oregon and California Trails. Although the exact site cannot be located, the general vicinity containing the site is a joint management responsibility of the Bureau of Reclamation and the Bureau of Indian Affairs.
The Camas Meadows Battle Sites, Idaho (6), N 44˚21’ W111˚53’ and N44˚24’ W111˚55’, consists of two sites, one on private and one on state land, both at Kilgore, Idaho. The battle sites were important in the flight of the Nez Perce away from the U.S. Army in 1877. At Camas Meadows Camp southeast of Kilgore on private land along Spring Creek, the Nez Perce conducted a pre-dawn raid on the military camp which resulted in capture of most of the army’s mules, forcing the army to halt and allowing escape to Yellowstone National Park and Montana. At Norwood’s Seige on state land northwest of Kilgore, soldiers built 23 rifle pits out of lava rocks and defended themselves against the Indians for several hours. Camas Meadows is one of 38 sites in Nez Perce National Historical Park.
The third site commemorates a nationally significant event in modern history. Experimental Breeder Reactor (EBR) –I Atomic Museum, Idaho National Laboratory (7), N43˚31’ W113˚0’, was the site where in 1951, a research facility produced the first usable amount of electricity from a nuclear reactor. In 1963, the reactor achieved a self-sustaining chain reaction using plutonium as fuel, thus demonstrating breeder technology. Following decommissioning of EBR-I, EBR-II, a successor reactor, ran from 1964 to 1994 and provided electricity to Idaho National Laboratory. An on-site museum also has exhibits on prototype aircraft nuclear reactors. The museum is located 18 miles southeast of Arco on US Route 20-26.
National Natural Landmarks (NNLs) in the Upper Snake River subsection highlight the volcanic geology left behind as the area moved over the Yellowstone hotspot. Big Southern Butte, BLM, Idaho (8), N43˚24’ W113˚2’, is four miles wide, making it the largest volcanic dome on earth. Its age is approximately 300,000 years old. This makes it the largest area of volcanic rocks of young age in the U.S. and qualified it for NNL status.
Great Rift System, Craters of the Moon National Monument and Preserve, Idaho (9), is unique in North America. Cracks in the earth extend for 62 miles, all included within Craters of the Moon National Monument and Preserve. There are three major lava fields, Carey, Craters of the Moon, and Wapi. The northern end of surface features are in the Pioneer Mountains and the southern end is the Wapi lava flow north of Minodoka Lake. Part of the Great Rift is included in the Craters of the Moon Wilderness area. Craters of the Moon is an IBA for violet-green swallow, mountain bluebird, raptors, and greater sage grouse. The northern end of the Great Rift is approximately at N43˚31’ W113˚37’ on Lava Creek and the south end is approximately at N42˚53’ W113˚13’ in the Wapi Lava Field.
Hagerman Fossil Beds National Monument, Idaho (10), N42˚49’ W114˚57’, is located on the west side of the Lower Salmon Falls Reservoir and is the world’s richest deposit of upper Pliocene (five million years ago) mammal fossils. Fossils of the first true horse (now Idaho’s state fossil), the Sabertooth cat, mastodon, bear, and camel are found here. The site also contains a portion of the Oregon Trail, and ruts can be viewed along the access road. The Bonneville Flood 15,000 years ago left enormous fields of rounded lava boulders in the Hagerman area and carved the high bluffs where the fossils are found. The site was discovered in 1928. The Visitor Center is on US Route 30 in Hagerman.
Hell’s Half Acre Lava Field, Bureau of Land Management (BLM), Idaho (11), N43˚19’ W112˚15’, is an unweathered fully exposed pahoehoe lava flow complete with rope coils. The NNL portion and main vent is on US Route 20 at milepost 287 (Twentymile) west of Idaho Falls. The Blackfoot Rest Area on I-15 also has trails through the lava field at both the northbound and southbound rest areas.
Niagara Springs, Thousand Springs State Park, Idaho (12), N42˚40’ W114˚40’, is located eight miles south from I-84 at exit 157 on road S1950E. This large spring discharges into the Snake River. It is part of the Hagerman IBA for nesting herons, eagles, and waterfowl.
North Menan Butte, BLM, Idaho (13), N43˚47’ W111˚58’, is located at the confluence of Henry’s Fork and the Snake River. These are the world’s largest tuff cones. A trail leads to the top of the butte. The south butte is privately owned. This late Pleistocene feature formed when a dike intruded into a shallow aquifer.
Additional sites in this ecological section are described at sites.google.com/site/enviroramble.
