How to make a rough gravel terrain? I need some help figuring out how to model some rocky ground. Basically, I want to model the Ludendorff Bridge and I'm in the process of trying to create the ballast-like area of the train tracks, for example: 

 

You can see a train track situated on the rocky ground I'm trying to create. 

How would I go about doing this? I've tried creating individual rocks and then dropping a bunch of them with the Drop To Ground add-on, but it doesn't really give the effect I'm going for.
A particle system with Dupli-group is probably a good way to go.

I'd start by creating a dozen or so rock templates. Using modifiers, you can come up with this pretty fast:



Then create a new plane that will serve as the base of where the rocks will go, and create a particle system to it. The particles system controls where the rocks will go, distribution, size, etc.