The Oregon and Northwestern Railroad (O&NW) is a defunct railroad in eastern Oregon in the United States. It ran 50.2 miles (80.8 km) from Hines north to Seneca, which is on the edge of the Malheur National Forest, over a total of 19 trestles.

Seneca is a city in Grant County, Oregon, United States. It is located in the Blue Mountains about 23 miles (37 km) south of Canyon City, on U.S. Route 395, on the edge of the Malheur National Forest. The population was 199 at the 2010 census.