Quick park and grab along the river highway
You are in the San Luis Rey River valley. You can park right before you get to the cache, but if traffic is heavy (usually on weekday afternoons) you might have a hard time going straight on through and will be stuck in the right turn lane, so keep that in mind. Cache is one of the usual suspects your experience has shown you to find at one of these locations, so log this one, have fun and drive safely.