The Double-O Ranch Historic District is located west of Harney Lake in Harney County in southeastern Oregon, United States. At one time, the Double-O Ranch covered over . The ranch was owned by Bill Hanley, a well-known cattle baron and Bull Moose progressive. In 1941, the United States Government purchased most of the Double O Ranch property and added it to the Malheur National Wildlife Refuge. The two remaining Double-O Ranch buildings are now listed on the National Register of Historic Places. Early history The Double-O Ranch is located in the Harney Basin of southeastern Oregon. Around 9,800 years ago, the Harney Basin was covered by a single great lake covering . Early inhabitants received abundant food from the birds, animals, and plants found in the wetland around the lake. About 3,500 years ago, small villages began to develop around it. Due to extended droughts beginning about 1,400 years ago, the lake and surrounding wetlands began to shrink. While there are no records of the earliest people to inhabit the Harney Basin, Native Americans used the wetland areas around Harney Lake for thousands of years before the arrival of European settlers. By the time Europeans began to explore the area in the early nineteenth century, the Northern Paiute people were well established in the Harney Basin. Hudson's Bay Company fur trappers were the first Europeans to visit the Harney Basin. Peter Skene Ogden passed through the area in 1826. Other fur trapping expeditions followed in the 1830s. Several military expeditions explored the area in the late 1850s. Major Enoch Steen was the first non-native to explore the Donner und Blitzen River area south of Harney Lake in 1860. Steens Mountain, that dominates central Harney County, was named in his honor. In the 1860s, the United States Army established a number of military outposts in the Harney Basin. The Double-O Ranch was established in 1875 by Amos W. Riley and James A. Hardin. It was one of the first permanent pioneer settlements in Harney County. In June 1878, during the Bannock War, the original ranch buildings were burned by a Bannock and Paiute war party. On 23 October 1878, the only pitched battle of that war occurred near Silver Creek on the northern edge of the Double-O Ranch. After the Bannock War, Riley and Hardin rebuilt the Double-O Ranch. They continued to operate the ranch until 1903, when it was sold