The following is from the book, Encyclopedia of Indian Wars, by Gregory F. Michno.
Cow Island in the Missouri River, in the southeastern corner of present-day Blaine County, Montana, was used as a landing for steamboats to unload their cargo for freighters to pick up, rather than risk the Dauphin Rapids, a troublesome stretch of river 18 miles upstream. Sgt. William Moelchert, 11 soldiers of the 7th Infantry, and 4 civilians were there to guard a government supply delivery when Chief Joseph's Nez Perces, heading toward Canada, reached the Missouri crossing at the island.
The Indians rode near, but Moelchert motioned for them to keep their distance. After some long-distance parleying, the sergeant let a few come in and gave them a side of bacon and half a sack of hardtack. They went away, but a short while later he heard a shot. One of his men, Pvt. Person, had not come into camp with the rest, and Moelchert surmised that the Indians had shot him. He prepared his troopers in the willows by the river, and at dusk, the Indians began to pepper their position with bullets. Through the night, the warriors tried several half-hearted attacks in the pitch dark. In the morning, the Indians took what supplies they waned and burned the rest. By 10 a.m. hey had moved out, up Cow Creek.
No Indians were reported hit. Two civilians and one enlisted man were killed.