Complex sentence: The landslide closed the main railroad for three months, and U.S. Route 6 and U.S. Route 89 for eight months, during which time the communities of eastern and southeastern Utah were cut off from the rest of the state.
Split into simpler sentences: The landslide closed the main railroad for three months, while U.S. Route 6 and U.S. Route 89 were closed for eight months. During this time, the communities of eastern and southeastern Utah were cut off from the rest of the state.