WALNUT CREEK, Calif. — That mustang in the rearview mirror turned out to be a real horse running on a Northern California highway — followed by a mule.

Commuters east of San Francisco on Monday were stunned to see a white horse and a brown mule running across Interstate 680.

Steve Burdo with Contra Costa County Animal Services says the animals broke through a fence about a mile away.

The pair adhered to the vehicle code and used an on-ramp to enter the highway.

Authorities shut down lanes shortly before 7:30 a.m. as motorists shot cellphone video and officers rounded up the four-legged fugitives.

Burdo says the horse, a gelding named Striker, appears to have led the breakout. He says Hank the mule is more of a follower.