Was created on the 4th March 2011. It covers an area of 3650ha. This area is on the northern side of the Glen Davis Road, 8km east of Capertee and includes Mount Airly and Mount Genowlan. The park contains a great diversity of ecosystems, supporting several threatened plants and animals and two threaten ecological communities. It also contains heritage stone dwellings of New Hartley oil shale ruins near Airly Gap. Named after the Wiradjuri Elder, Charley Riley. Mugii is Riley's Wiradjuri name and means a Mopoke Owl, while Murum-ban means eldest son in the Wiradjuri language.
On the 14th September 2016 a further 274.2ha was added to the northern boundary. This addition results in the northern boundary adjoining the Capertee National Park.