 In downstream order, beginning at the headwaters, major tributaries of the Umatilla River are the North Fork Umatilla River and the South Fork Umatilla River, then Meacham, McKay, Birch, and Butter creeks.The name "Umatilla" is derived from the Native American name for the river, which was first recorded as "Youmalolam" in the journals of the Lewis and Clark Expedition and spelled in many other ways in early books about Oregon.The Umatilla River's headwaters lie in the Blue Mountains at the confluence of its north and south forks in the Umatilla National Forest of northeastern Oregon.