Idaho Geography: Mountains, Snake River Plain, and Hells Canyon

Idaho's geography is extraordinarily varied — from the panhandle's dense Selkirk and Cabinet Mountain forests (receiving 60+ inches of precipitation per year) to the Snake River Plain's volcanic basalt and desert to the central Idaho batholith (one of the largest granite intrusions in the US).

Northern Idaho Panhandle
The narrow panhandle north of the Salmon River is a forested extension of the Rocky Mountain ecosystem — the Selkirk and Cabinet Mountains receive the heaviest snowfall in Idaho. Lake Coeur d'Alene (25 miles long, crystal clear) and Lake Pend Oreille (65 miles long, 1,158 feet deep — one of the deepest lakes in the US) are the dominant geographic features. The St. Joe River — the highest navigable river in North America — drains this region.

Central Idaho Batholith
The heart of Idaho — a 12,000-square-mile granite batholith (the Idaho Batholith) forms the backbone of central Idaho. The Sawtooth Range, the White Cloud Peaks, the Borah Peak area, and the Salmon River Mountains rise from this foundation. The Salmon River (the "River of No Return") drains westward through a canyon only slightly less deep than Hells Canyon. The Frank Church-River of No Return Wilderness (2.4 million acres — the largest in the lower 48) occupies most of this region.

Snake River Plain
A crescent-shaped arc of basalt plain sweeping from southwest to northeast across southern Idaho — formed by the passage of the North American plate over the Yellowstone Hotspot over the past 15 million years. The plain is dotted with cinder cones, lava tubes, and volcanic features at Craters of the Moon. The Snake River has carved the American Falls Reservoir and Twin Falls' Shoshone Falls (212 feet — taller than Niagara) through the basalt.

Hells Canyon
On the Snake River between Idaho and Oregon — at 7,993 feet from rim to river, Hells Canyon is the deepest river canyon in North America. The canyon is deeper than the Grand Canyon. The Seven Devils Mountains on the Idaho side rise above 9,000 feet; the river at the bottom is at 1,000 feet elevation. The canyon is accessible by jetboat from Lewiston or by four-wheel-drive roads from the Riggins area.

Owyhee Plateau (Southwest Idaho)
A remote, rugged plateau of volcanic rock and river canyons in southwest Idaho and southeast Oregon — the Owyhee Canyonlands, carved by the Owyhee River, are some of the most remote terrain in the contiguous US. Few roads cross this landscape.