The jury found Angelo Fabiani Arroyo guilty of hit-and-run felony, but they determined he was not guilty of child abuse.
Fabiani faces up to seven years in prison if convicted.
Deputy District Attorney Marisa Di Tillio said the defendant walked away from the June 2, 2013, accident after unlatching a seat belt that was holding his son Valentino's car seat in place, sending the child headfirst into the concrete below.
The youngster was declared brain-dead eight days later.
"He (the defendant) left him there,'' the prosecutor told the jury. "He was reckless in what he did.''
Fabiani, 41, testified that he left the scene because he couldn't bear to see his bloodied son, whom he thought was already dead.
The two were headed to the home of the child's mother after a day at Mission Bay when the accident occurred about 8 p.m. The defendant said after leaving the scene, he walked 19 miles to his home in Imperial Beach.
For two days following the accident, Fabiani didn't call police or check on his son's condition, Di Tillio said. He was arrested around noon on June 4, 2013.
"He knew police were looking for him,'' the prosecutor said. "The whole city was looking for him. He only thought about himself.''
In the days after the crash, Fabiani went on a dating website and talked with friends on Facebook about getting across the border into Mexico, Di Tillio said.
"I can't live with myself,'' Fabiani wrote in one Facebook message. "I've done the ultimate bad. I'm on the run from the law.''
Di Tillio said Fabiani was arrested as he made plans to meet a friend who agreed to drive him into Mexico.
The prosecutor said there was no evidence that the defendant was knocked unconscious in the accident and that his brain "shut down,'' as the defense claimed.
Defense attorney Allen Bloom argued that Fabiani should have been hailed as a hero for jumping in the back on his damaged pickup truck and trying to free his son, instead of being charged with a pair of crimes.
"What would she (the prosecutor) have him do?'' Bloom asked. "Would any of us done any differently? He tried to save his boy. Angelo's actions here were not reckless. They were heroic.''
Bloom said Fabiani was in shock when he left what he thought was his dead child and walked home to Imperial Beach in his flip-flops.
Fabiani's brain "shut down'' and didn't come back "online'' until about 40 hours later, Bloom told the jury.