The fog made driving dangerous in the Valley Monday morning.
The California Highway Patrol says shortly before 8:30 a.m. several cars crashed in the fog near Whitesbridge and Dickenson in Fresno County. One of them crashed into a mailbox.
The CHP says a few minutes later, there was a second crash in the same area. Those drivers had to be taken to the hospital but are expected to be okay.
Officers say both crashes were caused in part by fog and speed.
Fog is also being blamed for a crash involving an ambulance in Kings County.
Emergency Medical Services officials say just before 9 a.m. a car crashed with a big rig near 11th and Kansas.
A Kings County ambulance was called out, but just before it arrived, the ambulance crashed.
Investigators are not sure how this happened, but they do say conditions were extremely foggy and played a role in both crashes.
The people involved in the first crash were taken to Adventist Medical Center in Hanford. They were not badly hurt.
The two ambulance crew members were taken to Community Regional Medical Center in Fresno with what were described as severe injuries.