Double-O Ranch Historic District, Ranch complex in Harney County, Oregon, United States

The Double-O Ranch Historic District is a historic district west of Harney Lake in Harney County, Oregon, with two remaining ranch buildings listed on the National Register of Historic Places. The original ranch buildings were burned in 1878 during the Bannock War and later rebuilt by founders Amos W. Riley and James A. Hardin.

Amos W. Riley and James A. Hardin established the Double-O Ranch in 1875, one of Harney County's first permanent pioneer settlements. A Bannock and Paiute war party burned the original buildings in June 1878 during the Bannock War; the ranch was rebuilt and sold in 1903 to Bill Hanley, who bought it for $6 an acre. In 1941 the government paid the Hanley family $118,000 for 14,751 acres and added them to the Malheur refuge.

The ranch's name comes from the cattle brand featuring two connected O marks that identified multiple owners' livestock. The place reflects an era when large cattle operations served as social gathering points in this remote landscape.

The site sits roughly 25 miles southwest of Burns and is reached by driving through rural roads in the refuge. Access depends on wildlife refuge hours and conditions, so checking beforehand helps ensure a smooth visit.

The Double-O Ranch once stretched from its gate to the main house door for 8 miles (13 km). Bill Hanley hosted guests including Theodore Roosevelt, Will Rogers and painter Childe Hassam at the rustic retreat.