Peat formed at Slieve Gallion in the early Holocene period, around 10,000 years ago.[8] The radiocarbon dating of pollen has shown that there were plants in the area 10,000 years ago. 7,000 ago, the number of alder trees steeply increased.[8]
From the Middle Ages until the 20th century, gatherings were held on the mountain to mark the festival of Lughnasadh.[2] In recent decades, there has been an increase in the number of sheep grazing in the area, as well as an increase in mountain biking and hill walking, contributing to erosion.[8]
There was formerly a challenge walk/run from the village of Moneymore to the summit of Slieve Gallon, which took participants through idyllic countryside such as Cairndaisy glen and the Postmans Way. There is now a yearly mountain race from the foot of Inniscarn Forest to the mountaintop and back, which normally takes place on the last Saturday of September or the first Saturday of October. Organised under the Northern Ireland Mountain Running Association, this event attracts some of Northern Ireland's top athletes and hosted the British & Ireland Junior Mountain Running Championships in October 2006.[citation needed]
The sports of hang gliding and paragliding use Slieve Gallion. This site is considered a good starting point to go cross-country as there is little in the way of airspace restrictions in a downwind direction from its predominate flyable faces.[citation needed]
In 2019 a wind farm was constructed on its eastern side known as Crockandun wind farm.[citation needed]
Australian Gold firm Walkabout resources could collaborate with Koza UK to start a gold mine on the mountain. As of August 2020 the joint venture only holds a prospecting license and has not submitted plans for a gold mine.[citation needed] The project has been rejected by the district council of Mid Ulster.[citation needed]
