Federal regulators say a company responsible for a massive oil spill on the California coast a year ago didn't do enough to prevent pipeline corrosion and its operators didn't detect the spill quickly enough.

The Pipeline and Hazardous Materials Safety Administration said in its final investigation report Thursday that Plains All American Pipeline also didn't have adequate systems to detect the leak that spilled more than 120,000 gallons.

The report was issued on the one-year anniversary of a pipeline rupture that closed scenic Santa Barbara County beaches and is blamed for killing wildlife.

The agency previously said severe corrosion was the cause of the spill, but the new report goes into greater depth about failures to detect and prevent that corrosion and also operator error in detecting the leak.

Plains is facing dozens of criminal charges in Santa Barbara County Superior Court for the spill.