a state in the north-western US. Its popular name is the Gem State, because it has many minerals, including silver. It also produces a quarter of all the potatoes grown in the US. It was part of the Louisiana Purchase and became a state in 1890. Its capital and largest city is Boise. Idaho's attractions include the Rocky Mountains, Craters of the Moon National Monument and Hell's Canyon, which is the deepest gorge (= valley with steep sides) in North America.