Police and fire crews say the driver of a Mercedes got confused because the service gate to the wash was open for maintenance crews.
The woman drove past the workers and kept on going at 60 to 70 miles an hour from Glenoaks Boulevard to San Fernando Road at about 11 a.m.
Witnesses say she never used her brakes, but she was slowed down by all the steps covered in water in the wash. The car went down nine steps before her car eventually got stuck.
Witnesses said it was one of the most unbelievable things they had ever seen.
"It sounded like a big rig hitting something metal, and then it just kept on crunching it up and going ... it just kept going," said Lisa McCallister, who witnessed the incident.
The woman is being evaluated, but she did not appear injured. Police say she was not drunk.
The Mercedes remained at the scene for several hours after the incident, as authorities tried to determine what agency was financially responsible for getting the car out. Police say that the woman's insurance will have to pay for the costs.