The California Highway Patrol said it was called to a home in Santa Rosa after a child was somehow hit by a vehicle while riding his bike.
An ambulance was called the scene, but the four-year-old died at a nearby hospital, according to CHP.
The accident happened on a property on Bennett Valley Road around 1:30 p.m. The property appears to be a large sprawling hilly area when viewed on Google maps.
The boy was riding his bicycle alongside his uncle's pickup truck on private property in unincorporated Sonoma County when he veered into the vehicle's path, according to the California Highway Patrol.