Injury fears as spikes found on Rhondda mountain tracks
Concealed spikes left on tracks on Bwlch mountain in Rhondda Cynon Taff could soon cause a "nasty injury", an off-roading club has said.
The area is also popular with horse riders, cyclists and walkers.
The club, which found the spikes, told BBC Radio Wales' Good Morning Wales they looked as if they had been made "for the sole purpose of causing injury".
South Wales Police has launched an investigation.
Traps were left on a mountain near Caerphilly in January, leading police to issue a warning.
Michael Toseland, a marshal for off-roading events club Bonkas 4x4 Wales, said they have had issues with some rights of way being blocked.
He added: "A couple of our guys were out at the weekend and noticed some people looking like they were filling holes in and putting some quite nasty metal spikes in.
"They are burying them just under the surface of the soil, so if you stepped on them you'd get quite a nasty injury.
"I've never seen anything like this. It's quite a worrying thing. There's lots of dog walkers and children around there."
Mr Toseland said off-road drivers have a bad reputation, but insisted his club "always try to make sure we stick to the legal lanes".