Final answer:
The Chuckanut Formation was deposited during the Tertiary Period, which had a warm and humid climate. Based on the habitat requirements of Picea, the climate in the U.S. during this time was likely cool and moist.
Step-by-step explanation:
The Chuckanut Formation was deposited sometime during the Tertiary Period, which occurred from 66 to 2.6 million years before present.
The Tertiary Period was characterized by a generally warm and humid climate on Earth.
This climate allowed mammals to evolve and fill the ecological niches left by the dinosaurs.
Modern rainforests, grasslands, flowering plants, and insects were abundant during this time.
Based on the modern climate conditions and habitat for Picea, which is a genus of evergreen trees such as spruces, we can infer that the climate in the U.S. during the deposition of the Chuckanut Formation was likely favorable for these trees.
Picea species thrive in temperate and boreal regions, where they require cool temperatures and moderate to high annual precipitation.
Therefore, the climate in the U.S. during the formation of the Chuckanut Formation was likely cool and moist.