The woman was hit by multiple vehicles at about 6:15 a.m. on westbound I-580 just east of 14th Avenue.
Morgan said there were no disabled or crashed cars in the area and that it is unclear why the woman had entered the roadway. He said reports that she had jumped from an overpass are incorrect.
Several lanes of westbound I-580 were shut down so the CHP could investigate the death, he said.
"It's very slow traffic in the area," Morgan said at about 8 a.m.
All lanes were reopened at 8:07 a.m.