Sonoma Raceway officials are investigating "a piece of twine tied in what appeared to be a noose," that was found on the track's property on Saturday, president Steve Page said.
"Our staff, on-site business tenants and local law enforcement have been contacted and asked to share any information they may have," Page said in a statement. "Sonoma Raceway takes this incident very seriously and is dedicated to operating a facility that is welcoming to everyone."
Sonoma Raceway holds 47,000 fans, hosting NASCAR Cup Series events as well as the IndyCar Series. It was closed over the weekend when the noose was found.