WellPoint Health Networks Inc., one of California's biggest health insurers, offered to pay $266 million to buy Rocky Mountain Hospital & Medical Service Inc., the parent of Blue Cross Blue Shield of Colorado & Nevada. The offer includes $150 million that would be spent for charitable uses as part of the nonprofit Rocky Mountain's conversion to a for-profit company. An additional $16 million would go to Anthem Inc., a competitor to WellPoint that had offered to buy Rocky Mountain for about $165 million, WellPoint spokesman Peter O'Neill said. WellPoint is making the offer as it moves to expand outside of California, where it operates Blue Cross of California. Rocky Mountain said its board will convene to consider which offer to pursue. Rocky Mountain serves about 430,000 Blue Cross Blue Shield members in Colorado and 70,000 in Nevada. Shares in Thousand Oaks-based WellPoint fell $1.56 to close at $81.50 on the New York Stock Exchange.