Despite its vast area, only 7% of the county area is populated. The remaining area is occupied by rivers (7%) and mountains (87%). Mountains are composed of Central Mountain Range in the west and Hai'an Range in the east. The main rivers in the county are the Hualian River, Xiuguluan River and their branches. The plains stretch along the valleys between both mountain ranges with a width around . Due to the restriction of its landscape, Hualien people reside mostly on the alluvial fans of the Huatung Valley plains.