All four defendants had been named in an earlier indictment in Oregon charging them with conspiracy in a series of similar sabotage attacks in Oregon, California and Wyoming. Two are in custody in Oregon, and the other two were still at large.
The Vail blaze "really is a subset of the larger conspiracy," U.S. Attorney William Leone said.
The blaze left a mountain lodge, two restaurants and a few other buildings and ski lifts in smoldering ruins. A shadowy underground group calling itself the Earth Liberation Front claimed responsibility and said it had targeted Vail because it was expanding into potential habitat of the lynx, an endangered cat.
In a message sent to a radio station, it warned: "We will be back if this greedy corporation continues to trespass into wild and unroaded areas."
U.S. attorney's spokesman Jeff Dorschner wold not say how the defendants were connected to the crime.
Leone would not say whether the four indicted in Colorado were members of the ELF. The Oregon indictment, brought against 11 people, said some of them considered themselves members of ELF or the Animal Liberation Front.
Authorities say the ELF has caused tens of millions of dollars in damage across the country through sabotage. The FBI describes the group as one of the nation's leading domestic terrorist organizations.
Named in the indictment are Chelsea Gerlach, 29, of Portland, Ore; Stanislas Meyerhoff, 28, of Charlottesville, Va.; Josephine Sunshine Overaker, 31; and Rebecca J. Rubin, 33. Gerlach and Meyerhoff are in custody in Oregon. Authorities said the whereabouts of the others were unknown.
Each faces eight counts of arson. Each charge is punishable by five to 20 years in prison.
William C. Rodgers, who was identified by federal prosecutors as the mastermind of the Vail arson but was never charged, committed suicide recently in an Arizona jail after he was indicted in the string of attacks out West.
Meyerhoff's attorney had no comment. Gerlach's lawyer did not immediately return a call.
Vail Resorts Inc. has since rebuilt the lodge 11,000 feet above sea level, some 100 miles west of Denver.
In the Oregon indictments, the four were accused of a string of crimes, including the topling of an 80-foot electrical transmission tower and arson attacks on meat and timber companies, a car dealership and a Bureau of Land Management wild horse center.