Over the last few weeks various bikers - who are adhering to social distancing guidelines - have discovered obstacles, such as tree branches, which appear to have been deliberately placed across several trails on the hill.
The cyclists, who have decades of mountain biking experience between them, say they have never seen anything as serious or potentially life-threatening as the incidents of the last few weeks, the most recent of which was discovered on Wednesday (May 20).
They have also witnessed people who appear to be breaking social distancing rules by heading up Beinn Ghuilean in groups, as well as an increase in the amount of rubbish on the hill.
The bikers say they are unsure if the incidents are related but they do coincide with an increase in the number of people visiting the landmark.
Simon Freeman, who has mountain biked in Campbeltown for many years, said: 'Beinn Ghuilean has been a hive of daily exercise activity over the last few weeks and I'm sure that a walk or bike ride up there has eased the stress and anxieties of lockdown for many people. The weather has been fantastic and it has been great to see so many new faces up there.
'Unfortunately the increased usage has led to an increase in the amount of litter being left behind by a thoughtless minority, but I have also seen many individuals collecting other people's rubbish and taking it down the hill with them. If you are one of those people, then please know that as a community we all very much appreciate your efforts.
'The issue of trail sabotage has unfortunately reared its ugly head once again recently, with logs and branches being placed over bike trails in a direct attempt to cause mountain bikers to crash and injure themselves.
'The people who do this need to know how serious the consequences of their actions could be. How would they feel if somebody hit their obstacle, landed awkwardly and was paralysed or even killed?
'There has been an influx of new riders using the trails over these last few weeks, including a lot of youngsters. It is fantastic to see these young people keen to get outside and learn to ride more confidently, and we really enjoy encouraging them and helping them to get the most from the great facility they have on their doorstep.
'How would the saboteurs feel if it was one of these children that was seriously injured because of their act of vandalism?'
Andy Hunt, Forest and Land Scotland's west region manager, said: 'Given the COVID-19 lockdown, the majority of forest operations and staff inspections have been suspended in line with the current Scottish Government guidance as they are not regarded as essential work.
'We were not aware that any vandalism had occurred but it is clear that anti-social behaviour of this sort causes nuisance and harm, and we would urge anyone with any knowledge of these incidents to contact the local police.
'Anti-social behaviour of this kind is likely to endanger other people and may require the attention of the emergency services who are essential in providing critical care to the most vulnerable during this pandemic.
'We would urge everyone to follow the NHS and Scottish Government guidance and to behave responsibly. Additionally, this remains a live site for timber haulage so we would respectfully ask that all members of the public comply with the warning signage that has been erected for their safety.'
A Police Scotland spokesperson told the Courier that police are aware of the incidents on Beinn Ghuilean and are investigating, adding: 'Extra patrols will be undertaken in the area. If anyone has any further information please contact us on 101.'
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