Great Barrington is in the valley of the Housatonic River. The Williams River, Green River and several brooks also flow through the valley into the Housatonic. To the east of the river, several mountains of the Berkshires rise, including East Mountain (site of the Ski Butternut resort (also known as Butternut Basin) and a state forest), Beartown Mountain (and the majority of Beartown State Forest) and Monument Mountain. The Appalachian Trail crosses through East Mountain State Forest in the southeast corner of town. The southwest corner of town is the site of several country clubs and a fairgrounds.