FRESNO, Calif. (AP) — Authorities were searching a stretch of the Merced River for a 6-year-old boy after his older brother died when a current swept them away during a family outing in Yosemite National Park.

The boy is presumed dead. Other hikers pulled the body of his 10-year-old brother about 150 yards downstream from where family members had waded into the river to cool off Wednesday.

Their mother was hospitalized with a back injury after being pulled from the river, park spokeswoman Kari Cobb said.

“She went into the river but made it out,” Cobb said.

The names of the boys were not immediately released.

The family from Southern California was hiking near the Vernal Fall Footbridge, a vantage point on the Mist Trail where Vernal Fall first comes into view.

That portion of the hike can be perilous. The river falls 317 feet straight down to a narrow gorge filled with boulders the size of cars, then descends another 400 feet by the time it reaches the bridge.

Even when the river is moving slowly, the drop in elevation and narrow channel cause the water to move swiftly. The Merced River runs through the heart of Yosemite Valley.

The boys were part of a group of about 15 extended family members who made the short hike to the bridge, park spokesman Scott Gediman said. Signs at the trailhead warn that the river can be dangerous, but people often are drawn to the water’s edge.