Snake River

Although travelers on the Oregon Trail initially shunned the dry and rocky Snake River region, a flood of settlers followed gold discoveries in the 1860s, leading to decades of military conflict and the eventual expulsion of tribes to reservations.

The Snake River starts to the north of Two Ocean Pass near the southern border of Yellowstone National Park, about 9,200 feet (2,800 m) above sea level in the Rocky Mountains of Wyoming.

About 30 percent of the watershed is farmland; irrigated farming of potatoes, sugar beets, onions, cereal grains and alfalfa are dominant in the Snake River Plain, while the Palouse Hills of the northwest host mainly dryland wheat and legume production.

[30]: 606  The forests contain numerous designated wilderness areas, including the Sawtooth, Selway–Bitterroot, Frank Church-River of No Return, Gospel Hump, Hells Canyon, Teton and Gros Ventre.

[75] From about 11–9 Ma, crustal deformation related to the Yellowstone hotspot caused the western half of the Snake River Plain to sink, creating a graben-type valley between parallel fault zones to the northeast and southwest.

Upwelling magma caused the continental crust to rise, forming highlands in a similar fashion to the modern Yellowstone plateau and leaving behind enormous basalt flows in its wake.

As the hotspot migrated east relative to the North American Plate, the land behind it collapsed and sank, creating the geographic depression of the eastern Snake River Plain.

[79] The migrating Continental Divide tilted the regional slope such that drainage flowed west into Lake Idaho, whose water levels saw a significant increase about 4.5 Ma.

During this expansion, the Snake also captured the Bear River, which was only rerouted towards its modern outlet in the Great Salt Lake Basin about 50,000 or 60,000 years ago by lava flows in southeast Idaho.

[73]: 222–223  About 2.5 Ma, Lake Idaho reached a maximum elevation of 3,600 feet (1,100 m) above modern sea level, and overflowed northward into the Salmon-Clearwater drainage near present-day Huntington, Oregon.

Over a period of about two million years, the outflow carved Hells Canyon, emptying Lake Idaho and integrating the upper Snake and Salmon-Clearwater into a single river system.

About 15,000 years ago the lip of Red Rock Pass south of present-day Pocatello, Idaho abruptly collapsed, releasing a tremendous volume of water from Lake Bonneville into the Snake River Plain.

[85][86] The floodwaters then emptied through Hells Canyon; however, most evidence of their effects on the lower Snake River was erased by the much larger Missoula Floods that engulfed the Columbia Basin during the same period.

[85] Caused by the repeated collapse of an ice dam in western Montana, dozens of floods overflowed into the lower Snake River from the north, backing water as far upstream as Lewiston.

[90] Starting about 2200 BCE, people in the western Snake River basin began to adopt a semi-sedentary lifestyle, with an increased reliance on fish (primarily salmon) and food preservation and storage.

[96]: 44 Downriver of Shoshone Falls, salmon and their cousins such as steelhead trout – anadromous fish which spend their adult lives in the ocean, returning to fresh water to spawn – were a key food source for indigenous peoples, and were of great cultural importance.

[103] With horses, the Nez Perce were able to travel east of the Bitterroot Mountains to hunt bison, via the trail over Lolo Pass, which the Lewis and Clark expedition would later follow in order to reach the Snake and Columbia Rivers.

He wrote that "the passage by water is now proved to be safe and practicable for loaded boats, without one single carrying place or portage; therefore, the doubtful question is set at rest forever.

After a treacherous crossing of the Snake at Dug Bar, Hells Canyon on May 31,[124] the Nez Perce were pursued by the Army for over 1,000 miles (1,600 km) east, through Yellowstone before turning north through Montana, fighting several battles along the way.

In 1865, Thomas Stump attempted to pilot the Colonel Wright up Hells Canyon, making it 80 miles (130 km) upriver before hitting rocks in a rapid, forcing their retreat.

[137] The Idaho State Historical Society writes that "Perrine’s venture contrasted remarkably with private canal company failures that led to congressional provision for federal reclamation projects after 1902.

As a rare successful example of state supervised private irrigation development provided for in [the Carey Act] of 1894, Milner Dam and its canal system have national significance in agricultural history.

[138] Starting with Minidoka Dam in 1906, the project would grow over the next few decades to include major reservoirs at Jackson Lake, American Falls and Island Park, and a large network of canals and pump stations.

While that location offered greater power potential, the fishery supported by the Salmon River was considered too economically valuable to wipe out, and in 1964 the Commission chose to authorize the High Mountain Sheep project.

[152][151] By then, significant public opposition had formed against the high dam, as it would still block salmon migration to the upper Snake, and adversely affect wildlife and recreational values in Hells Canyon.

By 1966 it reached an agreement with the Federal Power Commission to move forward with the hatchery plan, and by 1967 both Oxbow and Hells Canyon dams had been completed, neither with provision for fish passage.

[120]: 100–103  While opponents continued to stall the project for a few more years, Washington Senator Warren G. Magnuson pushed through a budget amendment in 1955 to start construction on the first dam, Ice Harbor.

[30]: 608 Anadromous salmonids (Oncorhynchus), including chinook, coho, and sockeye salmon, and redband and steelhead trout, were historically the most abundant fish and a keystone species of the Snake River system.

About two-thirds of the Snake River Plain remains grassland or shrubland; however, much of this acreage is impacted by livestock grazing, and fire regimes have become more severe with the proliferation of invasive species like cheatgrass.

[174] In the context of shipping, while river traffic has declined in recent years, it remains important to the area's economy, and moving cargo by barge is cheaper and twice as fuel-efficient as diesel trains.

Wide view over a river valley surrounded by cliffs and shrub land
The Snake River flows through canyons in the Morley Nelson Snake River Birds of Prey National Conservation Area , south of Boise.
View of a river canyon surrounded by high, broken cliff faces
The Snake River in Hells Canyon
A freight train crosses a wide river on a steel bridge
The Union Pacific Railroad crosses the lower Snake River via the Joso Bridge near Starbuck, Washington .
A river flows through a mountain valley lined with autumn foliage
Fall colors along the Snake River upstream of the Henrys Fork, Idaho
View down a river entering a rocky canyon framed by high cliffs
Hells Canyon, the connection between the Snake River Plain and the lower Snake River drainage systems, formed about 2.5 million years ago from the overflow of Lake Idaho.
Map showing the extent of the Columbia River Basalt Province, a volcanic geologic province of the inland Pacific Northwest
The Columbia River Basalt Province covers a vast area of the inland Pacific Northwest.
A drawing shows a group of about 10 people on horseback, fording a river
Bannock hunting party fording the Snake River southwest of the Tetons, illustration by Frederic Remington c. 1895
Black and white photograph of two parallel waterfalls, dropping over a dark cliff face into a turbulent pool.
The cataracts of the Snake River forced early explorers and settlers to travel overland. This is Twin Falls, upstream of Shoshone Falls, as it appeared c. 1871.
Sketch of a square walled fort on a low hill above a waterway; in the foreground are a boat and a person fishing
The first Fort Boise (illustration by Major Osborne Cross, c. 1849) was an key supply point on the Oregon Trail.
A painted postcard shows a train crossing a bridge above a wide waterfall and turbulent river.
A train crosses the Snake River at American Falls, c. 1915. Railroads first reached the Snake River Plain in the 1880s.
View across a river, with a concrete dam on the left and a bridge on the right with a town on the opposite bank.
The first American Falls Dam (1927, rebuilt 1978) was constructed to store water for the federal Minidoka Project .
Aerial view looking upstream at an earthen dam and a reservoir stretching off into a mountain valley in the distance
Palisades Dam (1956) provides irrigation and flood control for the Snake River upstream of Idaho Falls.
Black and white sketch of a proposed dam project in a steep river canyon
Rendering of the Army Corps' proposed high dam in Hells Canyon
Front view of a concrete dam, with a river flowing off downstream to the left.
Hells Canyon Dam is the lowermost of three dams in Idaho Power's Hells Canyon hydroelectric complex.
A steamboat waits at a pier on a river bank while sacks of cargo are loaded.
Bags of grain are loaded on the sternwheeler Spokane at Lewiston, c. 1906.
Aerial view of a concrete dam on a river surrounded by rolling hills and farmland
Ice Harbor Dam (1962) was the first of four Army Corps dams constructed along the lower Snake River, and the final dam on the river before it joins the Columbia.
A wide, multi-stage waterfall, backed by dark cliffs, cascades into a rocky canyon
Shoshone Falls forms a complete barrier to upstream movement of fish in the Snake River, and was the historical upper limit of Snake River salmon and steelhead.
Detail view of a portion of a concrete dam, showing a fish ladder in between a spillway to the left and a navigation lock to the right.
Adult salmon and steelhead returning to the Snake River must surmount fish ladders at several dams, including this one at Lower Monumental Dam.
A river forms multiple channels as it winds through a forested floodplain in a wide valley
Riparian forest and floodplain habitat lines the Snake River in Swan Valley, east of Rexburg, Idaho.
A map showing the lower Snake and Columbia rivers, with locations of dams, cities and significant landmarks indicated
Map showing locations of dams on the lower Snake and Columbia rivers