IDIdaho Geography

Stand on He Devil Peak in the Seven Devils Mountains and the Snake River lies 7,993 feet below, which makes Hells Canyon the deepest river gorge in North America and about 2,000 feet deeper than the Grand Canyon. The canyon is also a state line. Idaho and Oregon divide along the river, so the boundary runs through the bottom of a gash almost a mile and a half deep.

That vertical drama repeats across the state. Borah Peak tops out at 12,662 feet in the Lost River Range. Lewiston, at the confluence of the Snake and Clearwater, sits at 710 feet. Nearly 12,000 feet separate the two, inside a state ranked only 14th by area.

Hells Canyon and the Seven Devils

The Snake enters Idaho from Wyoming, swings west across the southern plain in a long arc, then turns north and cuts down through basalt layers stacked by the Columbia River flood basalts. The Seven Devils rise on the Idaho side, the Wallowas on the Oregon side, and between them the river has no road for 79 miles. Three dams, Brownlee, Oxbow and Hells Canyon, block the upstream end, which is why salmon no longer reach the Snake above Hells Canyon Dam.

Further upstream near Twin Falls, Shoshone Falls drops 212 feet, a full 45 feet more than Niagara. Idaho's boundary with Oregon starts as a survey line running due north along the 117th meridian and only becomes the river once it reaches the Snake, so the state has one straight western edge and one carved one.

The night the Lost River Valley dropped

On the morning of October 28, 1983, a magnitude 6.9 earthquake broke the Lost River Fault near Mackay. The fault scarp it left runs about 21 miles along the base of the range and is still plainly visible from the highway. The valley floor dropped while the range went up, and Borah Peak, already the state high point, gained elevation in the process. Two children were killed by falling masonry in Challis. It remains the largest earthquake ever recorded in Idaho.

Idaho's mountains are not one range but dozens: the Bitterroots along the Montana line, the Sawtooths west of Stanley, the Lost River, Lemhi, Clearwater, Salmon River and Owyhee ranges among them. The Frank Church River of No Return Wilderness protects 2.367 million acres of that country, the largest contiguous wilderness in the contiguous United States.

A scar left by Yellowstone

The Snake River Plain sweeps in a smooth crescent across southern Idaho from the Oregon line to the Wyoming corner, and it is the track left behind as the North American Plate slid southwest over the hotspot now parked under Yellowstone. Everything about the plain, its flatness, its basalt, its aquifer, follows from that.

Craters of the Moon preserves the youngest chapter. Lava flows there erupted as recently as about 2,000 years ago along the Great Rift, leaving cinder cones, spatter cones and a black surface that NASA used to train Apollo astronauts in 1969.

Rivers that vanish, and a seaport in the mountains

The Big Lost River and the Little Lost River flow out of the mountains, reach the porous basalt of the plain, and simply sink. The water enters the Snake River Plain Aquifer and travels underground for a hundred miles or more before pouring back out of the canyon wall at Thousand Springs near Hagerman, where the discharge is large enough to support commercial trout farms.

The Salmon River earns its nickname of the River of No Return by running 425 miles from the Sawtooths to the Snake without a single dam, the longest undammed river contained entirely within one state in the lower 48. Almost all of Idaho drains to the Pacific through the Columbia system, with one exception in the southeast corner where the Bear River flows toward the Great Salt Lake and never reaches the ocean at all.

Idaho is landlocked, yet Lewiston is a working seaport. Barges load grain there and ride the locks of the Snake and Columbia 465 miles to the Pacific, making it the farthest inland port on the West Coast.

Six states, one province, and a 45 mile neck

Idaho touches more neighbours than almost anywhere in the region: Washington, Oregon, Nevada, Utah, Wyoming and Montana, plus British Columbia. The Canadian stretch is only about 45 miles long, the shortest international border of any state that reaches Canada.

The panhandle is that narrow because the Bitterroot crest hems it in from the east. Where Idaho meets Canada it is roughly 45 miles wide. Along the 42nd parallel at the bottom, a line fixed by the Adams Onis Treaty of 1819 as the northern limit of Spanish claims, it stretches about 300 miles. Lake Pend Oreille fills much of the northern panhandle, plunging to about 1,150 feet, deep enough that the Navy runs an acoustic research station at Bayview to test submarine designs a thousand miles from any ocean.

Two clocks, split by the Salmon River

Idaho runs on two time zones. The ten northernmost counties keep Pacific Time and the rest of the state keeps Mountain Time, with the dividing line running roughly along the Salmon River and slicing through Idaho County. Boise and Coeur d'Alene are in the same state but never on the same hour.

Climate splits along the same seam. The panhandle catches Pacific moisture and grows cedar and hemlock. The southern plain sits in a rain shadow and needs irrigation to farm. Idaho's record high of 118 degrees was set at Orofino in July 1934, and the record low of 60 below zero at Island Park Dam in January 1943, a spread of 178 degrees.

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