A HIGH MOUNTAINOUS PLATEAU
…The Continental Divide of North America runs roughly diagonally through the southwestern part of the park. The divide is a topographic ridgeline that bisects the continent between Pacific Ocean and Atlantic Ocean water drainages (the drainage from one-third of the park is on the Pacific side of this divide).
For example, the Yellowstone River and the Snake River both have their origin close to each other in the park. However, the headwaters of the Snake River are on the west side of the continental divide, and the headwaters of the Yellowstone River are on the east side of that divide. The result is that the waters of the Snake River head toward the Pacific Ocean, and the waters of the Yellowstone head for the Atlantic Ocean (via the Gulf of Mexico). There is a stream about six miles east of the Old Faithful area called “Two Ocean Creek”: it begins as a single stream which flows into “Two Ocean Pond,” from which two different streams emerge, one flowing to the Snake River and one to the Yellowstone River.
The park sits on a high plateau which is, on average, 8,000 feet (2,400 m) above sea level and is bounded on nearly all sides by mountain ranges of the Middle Rocky Mountains, which range from 10,000 to 14,000 feet (3,000 to 4,300 m) in elevation. These ranges are: the Gallatin Range (to the northwest), Beartooth Mountains (to the north), Absaroka Mountains (to the east), Wind River Range (southeast corner), Teton Mountains (to the south, see Grand Teton National Park) and the Madison Range (to the west). The most prominent summit in the plateau is Mount Washburn at 10,243 feet (3,122 m).
Just outside of the southwestern park border is the Island Park Caldera, which is a plateau ringed by low hills. Beyond that are the Snake River Plains of southern Idaho, which are covered by flood basalts and slope gently to the southwest (see Craters of the Moon National Monument).
The major feature of the Yellowstone Plateau is the Yellowstone Caldera; a very large caldera which has been nearly filled-in with volcanic debris and measures 30 by 40 miles (50 by 60 km). Within this caldera lies most of Yellowstone Lake, which is the largest high-elevation lake in North America, and two resurgent domes, which are areas that are uplifting at a slightly faster rate than the rest of the plateau.