PHOENIX — A Phoenix Parks and Recreation Department spokesman said city officials don't know who is putting piles of rocks and small boulders on mountain preserve trails — activity that some mountain bikers think may be intended to keep them from using trails.



Mountain biker Andrew James said he saw a man piling rocks on blind spots on a trail. According to James, the man claimed to be an authorized park volunteer and that he was blocking off an unauthorized trail.



Department spokesman Gregg Bach said there haven't been any reports of injuries from rocks being placed on trails but that the department is looking into the situation.



Bach said patrolling rangers remove items found to be blocking a trail.