Ralph F. Cox, former president and chief operating officer of Union Pacific Resources Co., has been appointed to the board of directors of Bonneville Pacific Corp., according to Raymond L. Hixson, chairman of the board,

Cox retired as vice chairman of Atlantic Richfield Co. in 1985 to becomne president of Champlin Petroleum Co., now Union Pacific Resources. He worked for ARCO for 31 years and was resident manager of the Prudhoe Bay oil discovery in Alaska.

Bonneville Pacific is an independent power producer involved in the development and operation of hydroelectric, geothermal, coal and natural gas generating facilities in all parts of the United States.