By the 1870's most of the nation had standardized on four feet eight and one half inch gauge, which had become a standard gauge, however there was one area that the large gauge was not suitable, and that was in the Rocky Mountains. The silver boom that had developed in the mountains created the demand for rails to reach the high off mines. Narrow gauge rails could go higher for less. That's what they did in Colorado. The most famous of the narrow gauges was the Georgetown Breckenredge and Leadville. The track looped over itself to reach the mines six hundred feet over Georgetown.

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