A 37-year-old Pleasant Hill man died Wednesday his SUV went off Highway 24 and struck a tree, the California Highway Patrol said.

Nathaniel Greenan was driving westbound in his white Lexus RX300 at 11:38 a.m., east of Camino Pablo when, for a reason under investigation, he went off the right side of the roadway, said Officer John Fransen.

The SUV crashed into a tree. Greenan was wearing his seatbelt but died from his injuries, Fransen said.

A dog riding in the vehicle survived the collision and was taken into the custody of county animal services.

Witnesses told the CHP that the SUV was traveling erratically before the crash, but an exact cause, including whether the driver was impaired, was still being determined, Fransen said.

Anyone with information about the fatal collision can contact the CHP Contra Costa field office at 925-646-4980 .