People enjoy the concrete floor of the Rio San Gabriel riverbed for many purposes. There are always skateboarders and bicyclists testing their skills on the dips and steep sides. I've seen dog owners playing fetch, and I've seen the occasional horseback rider.
But this was the first time I've seen the floor of the riverbed being used as a motorcycle maneuverability course. This biker was practicing his sharp turns at fairly high speed. I didn't see him touch a single cone.
And to finish things off, he paced a biker down the riverbed for a ways.