Boise is the state capital of Idaho. Population 26,130. Altitude 2739 feet. Located in the Boise Valley. 500 miles east of Portland and 400 miles northwest from Salt Lake City. On the line of the Union Pacific and U. S. Highway 30. B - Ada County Court House. O - View of Business District. I - Arrow Rock Dam. S - Boise River Bridge. E - Union Pacific Depot.