City

14,407 acres at the southern end of Idaho's Albion Mountains. Granite spires, fins, domes, and monoliths rise from the sagebrush, with some formations reaching the height of a 60-story building. The Almo Pluton granite is roughly 28 million years old; nearby Green Creek Complex rocks are more than 2.5 billion years old — among the oldest exposed rocks in the United States. Emigrants of the California Trail described the formations as "a city of tall spires," "steeple rocks," and "the silent city."