Marin mountain bikers are on edge this week after two cyclists discovered a spiked strip laid across a popular trail. The Marin Independent Journal reports that the apparent booby trap consisted of over 30 screws jammed through rubber, and was found on a trail that is approved for use by mountain bikers.

The four-foot long device was discovered Tuesday by a group of bikers in the White’s Hill Open Space Preserve, and was situated in such a way that the screws pointed up. “It was pretty scary,” cyclist Desi de Lenea told the Journal. “We’ve never seen anything like it. That’s why we had to pause. It was the first time something like that we both experienced.”

Mountain bikers have long been on the receiving end of opprobrium in Marin, with the Chronicle reporting that last April officials set up speed traps with radar guns to ticket cyclists traveling above 15 miles per hour on the shared trails. And while this is definitely not the first time someone has attempted to use spikes to apparently bring down cyclists, it may be the first time it's happened on what biking site Singletracks reports is a mountain bike-approved trail in Marin.

Although de Lenea removed the strip from the trail, and Marin sheriff’s deputies told the Journal that they're investigating, he remains concerned that the tension between hikers and mountain bikers remains unresolved.

"This homemade device could have crippled a bike or badly injured a cyclist," de Lenea wrote in a mass email, posted to Facebook, to cyclists warning of the discovery. "Sooner or later one of us will be badly injured by a booby trap or an intentionally placed log in the trail."

Related: Someone Is Spiking Roads In Woodside To Bring Down Cyclists