Never tried running on mulch... although now that you mention it, I kind of want to try running on it now.
My favorite place to bash are probably construction sites. It is very dusty (although I honestly don't mind the dust at all), but it is pretty hard packed with some soft sand in certain spots and then a very thin layer almost everywhere else. Whats nice about the local construction said is that it is on a slight incline, so you can just from each house foundation to the next. Its basically a really long and spread out row of stairs. There is also the road that is being built, and it is much lower than the foundation. Because of this, I can build step-up jumps from the street up on to the foundation. Its just an awesome place to bash. Unfortunately houses will be built there soon.
Here is a video of the construction site. Its pretty big, so there are many places to explore around that one spot the video was filmed in.
http://www.youtube.com/watch?v=95XQBo2qG_U