Amazon is in the process of testing its own delivery network to help complete the last stage of delivery in a package’s trip from factory to buyer, the Wall Street Journal reports. The e-commerce giant is using Candlestick Park in SF, as well as facilities in Los Angeles and New York, as bases of operation for Amazon trucks and contracted drivers. Self-delivery would be a huge step towards giving Amazon even more control over its sales empire, and yet another threat to brick-and-mortar retail. Amazon’s shipping costs are ballooning quickly, as the company gets bigger and serves more customers – last year alone it grew 29 percent, and relative to its total sales numbers, it’s been growing every year since 2009, the WSJ notes. Amazon can also use its own delivery team to more easily deliver same day, and to potentially deliver on holidays and weekends when service from carrier partners is not available or is cost-prohibitive.