Zimmer's husband of four months heard the crash, found his wife pinned under the car and called police.
When paramedics arrived, Hernandez had fled, Martinez said. Zimmer was rushed to a hospital where she was pronounced dead.
Orem police Lt. Craig Martinez said alcohol may have been a factor in the accident.
Hernandez appeared before 4th District Judge Steven Hansen on Monday morning, where the bail amount was set, according to Deputy Utah County Attorney Craig Johnson.
Johnson said his office asked for the high bail because Hernandez is classified as an "aggravated re-entry illegal immigrant" and is a flight risk. Johnson said Hernandez was deported in 2008, and is likely in the country illegally.
Hernandez will appear in court again next Sept. 3. He is being held in the Utah County Jail on suspicion of automobile homicide, though no charges have been filed as of Monday morning. Johnson said his office has until Hernandez's next court appearance to file charges.
Earlier Sunday, prior to the fatal accident, Lindon police cited Hernandez for intoxication and disorderly conduct while he was at a party, Martinez said. A friend gave Hernandez a ride home, according to Martinez, but Hernandez later decided to drive.
The Associated Press contributed to this report.