Bonanza is a city in Klamath County, Oregon, United States near Klamath Falls. The population was 415 at the 2010 census.
Bonanza is at an elevation of 4,127 feet (1,258 m) in southern Klamath County near the Oregon–California border. The city is at the east end of Oregon Route 70, a spur off Oregon Route 140. By highway, Bonanza is about 21 miles (34 km) from Klamath Falls and 300 miles (483 km) from Portland.
The Lost River flows through Bonanza. According to the United States Census Bureau, the city has a total area of 0.82 square miles (2.12 km2), all of it land.
This region experiences warm (but not hot) and dry summers, with no average monthly temperatures above 71.6 °F. According to the Köppen Climate Classification system, Bonanza has a warm-summer Mediterranean climate, abbreviated "Csb" on climate maps.
The city, in a farming district, was named after the Spanish word for prosperity (literally smooth sea), apparently because of the good springs found nearby. The Bonanza post office was established in 1875.
J. P. Roberts founded the community in 1876 and opened a store there. Bonanza was formally platted in 1878. By around 1900, it was considered the third most important city in Klamath County, after Klamath Falls and Merrill. Daily mail arrived by stagecoach.