Union Pass is a high mountain pass in the Wind River Range in Fremont County of western Wyoming in the United States. The pass is located on the Continental Divide between the Gros Ventre mountains on the west and the Wind River Range on the east. A triple divide exists nearby, where water may flow to the Mississippi River, Columbia River, or Colorado River. The pass was historically used by Native Americans and early mountain men including the Astor Expedition in 1811 on its way west. On the return trip, fearing hostile Indian activity near Union Pass, the Astorians chose a southern route and discovered South Pass.