Instead of starting at the parking area for the Gabrielino trail.. I usually would come over the dam from the Rose Bowl.. through that tunnel (walking at this point) and then ride on the dirt road toward JPL parking, stopping at Johnson's Rock for the drinking fountain to water-up, and then up the paved short connector to the trail.... If I go too close to those water ponds or whatever they are, it seems there are a lot of goatheads there..... and one time coming up the connector to the trail..well, you need to watch where you are going.
Also... worse than the snake are the employees coming out of JPL on their way home... they come out of there hot... they don't give a **** about bikers.