ArcLight Capital Partners LLC said Thursday it has acquired privately held Energy Corporation of America (ECA) and a trove of natural gas assets in the Appalachian Basin to form an exploration and production (E&P) company. The purchase price was not disclosed.

Greylock Energy, formed with a $400 million private equity (PE) commitment, is to own and operate the upstream and midstream assets. Greylock also is taking over an undisclosed interest in First ECA Midstream, a joint venture formed by ECA and PE giant First Reserve Corp. in 2011.

Greylock, headquartered in Charleston, WV, would have a patchwork of assets that span 900,000 acres in New York, Pennsylvania, West Virginia and Kentucky that includes more than 4,400 operated wells, 713,000 net deep acres and 2,600 miles of gathering assets. ArcLight said Greyrock would focus primarily on a core in Pennsylvania and West Virginia.

Denver-based ECA was founded in 1963 by John and Julie Mork. The company’s position once stretched more than one million acres from New York to Tennessee and included more than 5,000 producing wells and 5,000 miles of pipeline. While the company has operated in Appalachia for decades, it was never a major operator in the Marcellus or Utica shales.

However, ECA earned a name for itself in unconventional development as one of the first E&Ps in Appalachia to voluntarily disclose chemical additives used during hydraulic fracturing. It was also an early adopter of the dual-fuel system that used diesel and on-site natural gas to power rigs.

The founders’ son, Kyle Mork, who formerly served as ECA’s CEO, also would serve as chief of Greylock. He is to be joined by other members of the ECA management team.