A new campaign aims to protect ancient buildings and important habitats from the "menace" of off-road motorbikes and 4x4 vehicles in Denbighshire.
Burial chambers, hill forts and rare species are under threat from off-roaders churning up heather moorland.
Denbighshire countryside services is urging people to carry a special phone number to report illegal activity.
Offenders are warned their motorbikes and vehicles can be seized, and they can be fined up to £20,000.
The heather and hill forts project's moorland field officer, Nick Critchley, said: "We have a fantastic natural environment here which is under threat but we are fighting back.
"We are urging people who go out in our countryside to carry this number with them so they can blow the whistle on this illegal, dangerous and damaging menace.
"The message is don't leave home without it."
The area covered by the project provides habitat for rare species like the black grouse as well as important grazing for sheep.
Mr Critchley said Wales had lost 40% of heather moorland since World War II.
He added: "On Llantysilio Mountains, illegal bikers have created a race track that is damaging the ramparts of an iron age hill fort at Moel y Gaer that was here before the Romans arrived, and the track crosses a bronze age burial mound that is over 4,000 years old."
The scheme covers the Clwydian range area of outstanding natural beauty, the Horseshoe Pass and Llantysilio Mountain, part of the Ruabon/Llantysilio Mountains and Minera site of special scientific interest.
It also includes the Berwyn and South Clwyd Mountains special area of conservation.
The number campaign, featuring the phrase "don't leave home without it", is backed by North Wales Police, Countryside Council for Wales and Forestry Commission Wales.
The police telephone number is 0845 6071002 for English language callers or 0845 6071001 for Welsh language callers.