Thousand Oaks-based independent fuel retailer USA Petroleum Corp. plans to sell 122 of its California gas stations to the oil industry giant Chevron USA Inc. for an undisclosed sum. The majority of the stations on the selling block are USA brand discount gas stations, with a small number operating under the Shell and Chevron nameplates. Under the terms of the deal, which awaits Federal Trade Commission approval, those stations will be upgraded and turned into either Chevron or possibly Texaco brands. Chevron USA, a subsidiary of San Ramon-based Chevron Corp., operates 1,500 Chevron or Texaco gas stations in California.