Yellowstone has 67 mammal species. Best wildlife viewing: 1) Lamar Valley (NE corner) — 'America's Serengeti' for wolves, bears, bison, elk; best at dawn/dusk; 2) Hayden Valley (central) — bison herds, grizzlies; 3) Antelope Flats — pronghorn; 4) Old Faithful area — bison wander geyser basins; 5) Roosevelt Lodge — black bears in trees. Safety: maintain 100 yards from bears/wolves, 25 yards from other animals. Carry bear spray, hike in groups. Bring binoculars and spotting scope. Best months: May-June (newborn animals), September (rut, fewer tourists). Wolf packs: Junction Butte, Lamar Canyon. Grizzly viewing: open meadows in spring/early summer. Never approach bison — they appear slow but charge at 30 mph.