A golf course groundskeeper in northern California died Thursday when a grass mower he was riding went off a 20-foot embankment into a creek bed at the golf course, Mill Valley (Calif.) police said Friday.

Police identified the man as 36-year-old Earl Milligan of Rohnert Park. The accident was discovered around 11 a.m. near the ninth tee at Mill Valley Golf Course, police said.

Milligan was found beneath the mower and was pronounced dead at the scene. He worked for the city-owned course for 15 years, according to the Parks and Recreation Department. He leaves a wife and middle-school-age daughter.

State workplace safety officials are investigating the accident, police said.