SYLVA, N.C. -- Authorities closed a popular North Carolina park after a runner impaled his foot on a nail that they believed was purposely placed.

CBS Spartanburg, S.C. affiliate WSPA-TV reports a search of the 1,100-acre Pinnacle Park in Jackson County, about 162 miles west of Charlotte, turned up 40 nails hammered into tree roots and logs since Saturday.

Brian Barwatt, an engineer with the N.C. Department of Transportation and the director of a trail race in Pinnacle Park in March, said someone hammered 4-inch long galvanized nails and left them sticking out one-half to 1 inch, and at an angle. One person was hurt and another stepped on a nail that went through his shoe but didn’t hurt his foot.

Crews used leaf blowers and metal detectors to try to find any other nails, WSPA says.

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Officials are trying to make sure the trail is safe ahead of the Black Rock Summit race on March 18, the station adds.

The park was re-opened Tuesday, reports a local newspaper, the Citizen-Times.

A $1,000 reward was offered for information leading to the arrest and conviction of those responsible.