A hit-and-run driver who injured four bicyclists at a West Marin benefit ride was sentenced to 18 months in prison.

Aaron Michael Paff, 22, of Novato, drove his Dodge Ram truck into the cyclists in October on Point Reyes-Petaluma Road just west of Hicks Valley Road. The cyclists were participating in the Jensie Gran Fondo of Marin, a ride that benefits the Marin County Bicycle Coalition.

Witnesses said the truck intentionally swerved to the right to swipe the cyclists, police said. One witness estimated the truck’s speed at 65 to 70 mph.

The injuries to the cyclists included a spinal fracture, a dislocated elbow, a dislocated shoulder, a broken finger, head injuries and other wounds.

A passing motorcyclist who recorded the incident on a helmet camera provided the footage to the California Highway Patrol, leading to Paff’s arrest.

When police searched his damaged truck, they found “more than 20 Lagunitas beer bottle caps in the driver’s side door pockets, front floor, the rear seat and floor, and inside the passenger side door pockets,” according to a report by the Marin County Probation Office.

Paff told authorities he did not strike the cyclists intentionally, the report said. Paff said he had stayed up the prior night with friends, decided to drive up the coast that day and then nodded off at the wheel on the way home. He said he fled after the collision because he panicked.

Paff, a former Marin Municipal Water District employee, was charged with four felony hit-and-run counts. The potential term was five years in prison.

Last month he accepted a plea offer and admitted to two of the charges. The prosecution also dismissed a separate pending hit-and-run case in which he allegedly damaged a Novato shopping center with his truck and had an open alcohol container in the vehicle.

Judge James Chou sentenced Paff on Monday to three years in prison, but the sentence will be served at half-time under state sentencing guidelines. The plea deal called for the maximum term out of a range from 16 months to three years.

Paff had no prior convictions before the hit-and-run case.