SAN DIEGO (CNS) - A hit-and-run motorist, who was under the influence of alcohol and drugs when he struck a community activist removing graffiti in Mission Beach, pleaded guilty Wednesday to gross vehicular manslaughter while intoxicated.

Jonathan Domingo Garcia, 23, faces a maximum of 15 years in state prison when he is sentenced Aug. 30.

According to testimony at a preliminary hearing in April, Garcia was fleeing from another motorist he had rear-ended at North Jetty Road and Mission Boulevard around dusk on Feb. 12 when he stopped at a stop sign, then accelerated, hitting 69-year-old Maruta Gardner near the curb.

Gardner's husband said his wife was putting her Kindle reading device in the basket of her tricycle -- which was parked in the road -- when she was struck.

Garcia drove off and pulled into a parking lot, then drove back past the crash scene. A police officer followed Garcia and pulled him over.

About three hours before the crash, Garcia and a friend were seen slashing tires on cars a few blocks away, according to testimony.

A detective testified that Garcia admitted drinking beers and smoking marijuana that day.

Garcia's blood-alcohol content was measured at .079 percent after the collision, and marijuana and depressants were also in his system, said Deputy District Attorney Steven Schott.

Gardner, a former principal at Mission Bay High School, was honored by the San Diego City Council last year, which declared Nov. 3 "Maruta Gardner Day.''