The south and west slopes of Mount Jefferson drain into Hell Roaring Creek, thence into Red Rock Creek, the Red Rock River, the Beaverhead River, the Jefferson River, the Missouri River, the Mississippi River, and into the Gulf of Mexico.
Brower's Spring, the source of Hell Roaring Creek, on the mountain's east flank in Montana, is considered the absolute headwaters of the Missouri River.[3]
The northeast slope of Mount Jefferson drains into the South Fork of Duck Creek, thence into Henrys Lake, the Henrys Fork of the Snake River, the Columbia River, and into the Pacific Ocean.
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Nell, Donald F.; Demetriades, Anthony (2005). "The True Utmost Reaches of the Missouri". Montana Outdoors (July–August, 2205). Montana Fish, Wildlife and Parks. Retrieved 2008-04-08.
Northwest aspect of Mount Jefferson seen from Widgeon Pond, with Nemesis Mountain slightly right
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