J. C. Adams Stone Barn, Stone barn in Sun River Valley, Montana.

J. C. Adams Stone Barn is a Romanesque Revival barn of stone and wood about 1 mile northeast of Sun River, Montana, just south of U.S. Route 89. Its main section housed cattle, the west wing held horse stalls and tack, and the east wing stored wagons and had a cooled meat room. The second floor stored hay.

J. C. Adams began building the barn in 1882, hiring two Swedish immigrant stonemasons and Canadian-born foreman William Bruce; it took nearly three years and cost over $10,000. The single-piece stone arches were imported from St. Louis and shipped by steamboat to Fort Benton. The Sun River Press called the finished barn the "Marvel of Montana."

The barn's name comes from James Calvin Adams, who built the Sun River Ranch and held a roller skating party on the second floor to mark the barn's completion. Fort Shaw soldiers also held roller skating parties and formal functions there, and the second floor sometimes housed stagecoach passengers.

This location is in rural Montana and is best reached by car, as it is a historic site in a farming area. Visitors should be prepared for changing weather and should check accessibility beforehand.

This is the only building of its architectural style west of the Mississippi River in the entire country, making it a rare construction specialty. This exceptional status makes it notable for anyone interested in how building traditions varied by region.