Hills are elevations of the earth's surface that have distinct summits, but are lower in elevation than mountains. Hills may be formed by a buildup of rock debris or sand deposited by glaciers and wind. Hills may be created by faults. Faults are a slight crack in the earth which can cause earthquakes.
Hills are easier to climb than mountains. They are less steep and not as high. But, like a mountain, a hill will usually have an obvious summit, which is its highest point. According to the U.S. Geological Survey, there is no official difference between hills and mountains.