Sherburne County authorities say a 13-year-old Coon Rapids boy died this weekend after his snowmobile went over a snow bank and hit some trees. Sheriff Joel Brott says Mitchell Johnson was unconscious and had head injuries when paramedics arrived at the Sand Dunes State Forest parking lot, about three miles west of Zimmerman, on Sunday. He says Mitchell was wearing a helmet but efforts to revive him failed. The sheriff says investigators believe Johnson crossed the parking lot, went airborne after hitting a snow bank and couldn’t turn the snowmobile to avoid the trees.