SAN MATEO, Calif. -- A 66-year-old man who died while biking to work on the Bay Area's Bike to Work Day on Thursday was identified Friday by the San Mateo County coroner's office.

Joseph Walter Castillo, of San Mateo, apparently crashed his bicycle into a wood fence sometime between 5 and 6 a.m. in the northwest corner of Coyote Point Park near the Peninsula Humane Society, San Mateo County Parks and Recreation Director Dave Holland said.

The man, who was wearing a helmet when he crashed, was pronounced dead at the scene.

"What caused him to ride into the fence we don't know," Holland said Thursday, but added authorities speculated the man might have had a medical condition.

It was unknown whether an autopsy would be conducted on Castillo, according to the coroner's office.

The crash is Coyote Point Park's first reported fatal bicycle collision, according to Holland.

Thousands of Bay Area residents rode their bicycles to work Thursday in celebration of the region's Bike to Work Day.