A bus driver discovered the Toronto woman at 1:30 a.m. on Proudfoot Trail.
She had "suffered obvious trauma" and was taken to Hamilton General Hospital where she is in stable condition, police said in a statement. Police say she may have been hit by, or fallen from, a moving vehicle.
Sgt. Paul Davies with the Halton Police Collision Reconstruction Unit says the woman and a female companion were dropped off in the area by a taxi cab.
"We don't know what happened from the time the young ladies departed company till she was found. But what we do know [is] that when she departed company with her friend she was still in the cab, so, that's why the cab driver, it's very important that we speak to him."
Police are looking to talk to the driver of a white Toyota Camry taxi with a fleet number 2013 or 2310.
They are also appealing to the Toronto taxi cab community for their help with the investigation.