Top photo: A "bison jam" in Yellowstone's Hayden Valley—traffic gridlock caused by tourists moving through a bison herd—is a common occurrence in summer.  Image courtesy Jacob W. Frank/NPS.  Middle photo::  Summer crowds move along the boardwalks encircling Old Faithful Geyser and other features in the Upper Geyser Basin. Image courtesy Neal Herbert/NPS.  Immediately above here:  Visitors from around the world wait for Old Faithful to erupt. Image courtesy Jim Peaco/NPS
Top photo: A "bison jam" in Yellowstone's Hayden Valley—traffic gridlock caused by tourists moving through a bison herd—is a common occurrence in summer. Image courtesy Jacob W. Frank/NPS. Middle photo:: Summer crowds move along the boardwalks encircling Old Faithful Geyser and other features in the Upper Geyser Basin. Image courtesy Neal Herbert/NPS. Immediately above here: Visitors from around the world wait for Old Faithful to erupt. Image courtesy Jim Peaco/NPS