The Israel River rises near the foot of Mount Adams, at the juncture of Castle Brook and Cascade Brook. With its numerous tributaries, the river drains the northwestern slopes of Mount Adams and Mt. Jefferson in the Presidential Range, the northern slopes of the Dartmouth Range, and the southern slopes of the Pliny Range. The larger tributaries include the South Branch, The Mystic, Castle Brook, Cascade Brook, Stag Hollow Brook, Stanley Brook, Priscilla Brook, Alder Brook (also called Crawford Brook), Red Brook, Mill Brook, Garland Brook (which still turns a working saw mill) and Otter Brook.