Do you carry pepper spray?
I should get some, though there are many situations where it isn't so useful anyway (attacker with a gun, being outnumbered which I was in this case, or being overpowered and having it used against you). I don't normally go to such unoccupied areas alone. I expected this part of the trail to be similar to the other part (very developed and tons of people running/biking) and it was not. There were houses near (within earshot) the parking area, but not visible with the leaves out. I also don't think I was in any physical danger - they retreated into their car pretty darn quick when they saw I was coming back. My phone was on my person, so had they actually been IN my car I would have ridden past and then called the police.
It's also possible they were doing something entirely different but still illegal - looking for a place to hide drugs for pickup or something, and just happened to be parked right there.
I still feel more safe in a park than I do in most of the cities around here.