Colorado was badly hit when the Yellowstone Supervolcano erupted due to falling ash.Denver eventually was evacuated but the loss of life was in the hundreds of thousands. Areas further east and south were hanging in but barely.
In the aftermath of the Krolp invasion, Colorado became the center of the rump United States. Grand Junction became the de facto national capital. When the U.S. launched its failed uprising to prevent the Krolp from stripmining in Utah, the center of government was briefly transferred to Craig, Colorado.