The green light allows Alton to move ahead with its expansion; its proposal includes the lease and development of as much as 49 million tons of untapped coal reserves over about 25 years.

The block neighbors its existing Coal Hollow mine, which was given a permit in 2011 to operate on private and state land.

According to reports in the Associated Press and regional newspaper the Deseret News, the state’s high court ruled against a challenge brought by the Sierra Club’s Utah chapter and other environmental groups that argue0 state officials did not assess the impacts of Alton’s growth proposal.

In the 22-page decision handed down Tuesday, the court said Utah regulators satisfied state outlines to monitor the operation for water pollution in local waterways.

According to the News, lengthy cultural resource surveys were completed in the permit area as well as 3000 acres adjacent to the site.

The justices also said the company performed sufficient hydrologic studies within state and federal regulations that met environmental requirements.

The mine produces coal for Utah's Intermountain power plant, which provides the Los Angeles Department of Water and Power with more than a quarter of its electricity.

In June, Alton said the draft EIS noted the operation would generate coal needed to help meet the nation's energy needs but it also stated, "there would be an adverse impact to recreation and adverse impacts to sense of community, social wellbeing and tourism-related businesses".

Local press reported earlier this year that the operation would run 24 hours a day, six days a week, with 300 tractor-trailer trucks moving through the town of Panguitch daily to remove 50 million tons of coal.