The topography of the state is roughly defined by the Continental Divide, which splits much of the state into distinct eastern and western regions. Most of Montana's 100 or more named mountain ranges are concentrated in the western half of the state, most of which is geologically and geographically part of the Northern Rocky Mountains. The Absaroka and Beartooth ranges in the south-central part of the state are technically part of the Central Rocky Mountains. The Rocky Mountain Front is a significant feature in the north-central portion of the state, and there are a number of isolated island ranges that interrupt the prairie landscape common in the central and eastern parts of the state. About 60 percent of the state is prairie, part of the northern Great Plains.