The never-dammed Yellowstone River flows through the Paradise Valley and separates the eastern Absaroka Range and the western Gallatin Range. The valley starts narrow, squeezing through Yankee Jim Canyon  near Yellowstone National Park, then broadens enough for ranches to spread out on the valley floor.
Yellowstone’s volcanoes spat out the Absaroka Range—a high lava field with relief etched by erosion from water and glacial ice. The Absarokas are lush wet mountains, more characteristic of western Montana than the dry peaks east of the Continental Divide. The same Yellowstone lava flows covered folded sedimentary rocks of the Gallatin Range.