The Mesozoic Era in the Teton region was a time of alternating marine,
transitional, and continental environments. Moreover, the highly
diversified forms of life, ranging from marine mollusks to tremendous,
land-living dinosaurs, confirm and reinforce the story of the rocks.
Living things, too, were in transition, for as environment changed, many
forms moved from the sea to land in order to survive. It was the time
when some of the most spectacularly colored rock strata of the region
were deposited.