Wikipedia wrote:
On April 30, 1966, two days after the publication of his novel, Fariña attended a book-signing ceremony at a Carmel Valley Village bookstore, the Thunderbird. Later that day, while at a party to celebrate his wife Mimi's twenty-first birthday, Fariña saw a guest with a motorcycle, who later gave Fariña a ride up Carmel Valley Road, heading east toward the rural Cachagua area of Carmel Valley.
At an S-turn the driver lost control. The motorcycle tipped over on the right side of the road, came back to the other side, and tore through a barbed wire fence into a field where a small vineyard now exists. The driver survived, but Fariña was killed instantly. According to Pynchon's preface to Been Down..., the police said the motorcycle must have been traveling at 90 miles per hour (140 km/h), even though "a prudent speed" would have been 30 miles per hour (48 km/h).
Fariña is buried in a simple grave, its marker emblazoned with a peace sign, at Monterey City Cemetery, in Monterey, California.