SEATTLE — A 12-year-old Washington state boy was killed Saturday when a log rolled over him during a Boy Scout outing in the Olympic National Forest, according to the Jefferson County Sheriff’s office.

The boy, of Silverdale, and three other Scouts were trying to roll the log down a steep boulder field into Lena Lake at about 9 a.m. Saturday when a root ball at the end of the log snagged the boy’s jacket, knocking him down.

The log, which measured about 2 feet in diameter, rolled over him, causing massive head injuries, said sheriff’s Deputy Joe Nole.

Two Scouts ran about a half-mile from the lake back to the Lena Lake Campground to summon help while the boy’s 14-year-old brother stayed with him.

The boy’s father, a doctor who accompanied the boys on the trip, went to the accident scene and administered CPR to his son while another adult hiked three miles from the camp to the Lena Lake trailhead and then drove several miles for a cellphone signal to call 911, Nole said.

“We have nothing to indicate it was anything other than a tragic accident,” he said.

The Scouts, most of whom live in Silverdale, arrived at the campground Friday night. The boys were out exploring when the accident occurred, Nole said.

More than three dozen rescuers, most of them volunteers, responded to emergency calls for help.

Search-and-rescue teams in Jefferson County were dispatched to investigate an unknown emergency in the wilderness at about 9:20 a.m. An emergency beacon had been activated by a Federal Way man who was hiking in the area with his 6-year-old son and learned of the accident.

The emergency beacon helped the teams pinpoint the accident location, Nole said.

Rescuers in Mason County were dispatched separately based on the 911 call. It took rescuers about three hours on foot to reach the remote camping area west of Eldon, a small town on Hood Canal located 12 miles north of Hoodsport.

A helicopter airlift was deemed too risky because of bad weather.

Nole said a faster response by emergency personnel would not have saved the boy. He also said the 10 Scouts and four leaders in the group were experienced and prepared for the wilderness trip.

Early reports on the accident mistakenly said a tree had fallen on the boy while he was hiking with his father.