The crash happened at about 5:40 a.m. as the motorcyclist, who was riding a Kawasaki bike, tried to enter northbound I-680 from Mission Boulevard, California Highway Patrol Officer Steve Creel said.
Witnesses reported that the bike appeared to be traveling at 70 to 75 mph as the rider prepared to merge into highway traffic, which is not heavy in the northbound direction at that hour, Creel said.
As the rider rode up the on-ramp, smoke was seen coming from the bike, and the rider veered left over a raised median that separates the on-ramp from the highway, Creel said.
He was ejected from the motorcycle and landed on the right shoulder of the highway. The bike came to rest in the right lane.
The man was pronounced dead at the scene.
The CHP is still investigating what caused the crash, Creel said.
The right lane of the highway was closed as the accident was cleared.
