This county comprises a large part of the narrow portion of Idaho that extends northward to the U.S./Canada border. Form the summit of the Continental Divide on the east the county extends west halfway across the State. It lies in the greatly dissected platue region of the State, which is charicterized by deep valleys seperated by high, timbered divides.
The county is about 75 miles in greatest lenght from north to south. At the northern end it is only about 12 miles wide, but the eastern border travels southeastward , and along its southern border it is nearly 60 miles wide. Ore deposits were first discovered in 1878.
