The drive between Belfort and the Frederick Mine edges along a shale face. Here, timberline is clear and a blue sky abounds. Due to light traffic and stable roadbeds, the Sweetwater routes are readily accessible in a modern 4x4. At 10,000 to 11,000 feet, low range gearing is the place to be. Horsepower drops 3 to 5 percent for each 1,000 feet above sea level, nearly halving an engine's power at this elevation -- unless turbocharged.