Macerich Co. said it bought two shopping malls, one in Modesto and one in Billings, Mont., for $118.2 million in cash and debt. The sellers weren't identified. The purchase of the Vintage Fair Mall in Modesto and Rimrock Mall in Billings, which contain a total of 1.65 million square feet of space, boosts Macerich's portfolio to 23 malls and shopping centers with 16.6 million square feet of space. It also brings to $450 million the amount the Santa Monica-based company has spent over the last 12 months expanding its holdings. Macerich paid $26.8 million in cash and assumed $88.4 million of mortgage debt and $3 million in other liabilities in the purchase of the two malls.