"There were no barriers at all," Jeff Talbott, inland division chief for the California Highway Patrol, told the Riverside Press-Enterprise.
That sounds like the idiocy that used to happen in European rallying in the ‘80s. You see video from back then and these one-lane dirt roads are packed six deep with spectators—some even crossing the roads or running out right in front of the cars—while the cars are screaming through powersliding at 100+ mph on the ragged edge. It took a couple of crashes like this one until the organizers (now the WRC) got their heads straight and did a better job of controlling the crowds.
This looks like footage from the 2009 California 200 (warning, a little raunchy right at the end):
Some surprisingly big crowds there at points.