William Flint II was riding downhill on South Park Drive near the Grizzly picnic area at about 2 p.m. when his bicycle drifted into oncoming traffic, police said.
He crashed into the side of a 2003 Ford Expedition sport utility vehicle.
The driver of the SUV, with help from an on-duty park employee, rendered aid while they waited for paramedics to arrive.
Flint was taken by helicopter to John Muir Medical Center in Walnut Creek, where he was pronounced dead, police said
