A utility that bought a 2,160-mile natural gas pipeline network serving northwest Colorado, Wyoming and Utah early this year for $1.9 billion is selling it already, unloading it at a loss of up to $425 million.

Southwest Gas Holdings Inc. (NYSE: SWX) is selling the MountainWest Pipelines network, what had previously been called the Dominion Questar and Overthrust pipelines, to Tulsa, Oklahoma-based pipeline giant The Williams Companies Inc. (NYSE: WMB) for $1.5 billion in value, subject to some future adjustments, the companies said.