For the Crow tribe, the events of March 1880, on which Mr. Aaberg has focused his research, proved devastating. That was when a draft agreement from Washington was read aloud to tribal leaders for the first time here, at a compound that served as the arm of the federal government on the reservation.

The document ultimately forced the tribe, which once dominated a vast swath of Montana, onto a smaller reservation. It echoed a theme that scarred the West again and again as white settlers coveted lands that Indians had been promised but did not seem to be using: new document, new constriction of space.

What made the story even worse for the Crow is that they had allied with Gen. George Armstrong Custer against the Sioux and Northern Cheyenne only four years earlier at the Battle of the Little Bighorn — 100 miles east of here — and might have expected a reward, Mr. Aaberg said, or at least fairer treatment. The compound was abandoned in 1883 after the agreement was signed, because this spot, about 50 miles southwest of Billings, was no longer on the reservation.