Aah - I see now. I misinterpreted what you meant by sliding rocks.
Hmm. There are no direct tools to achieve this available right now. I had an additional “flow by terrain” device that would be ideal for this kind of thing but it didn’t make the cut for Alpine Lakes release. You could possibly hack something together using the Select Wetness device, which accumulates downslope flow, and add/remove material based on that flow. You would put your boulder mask into the precipitation input, invert the model so that uphill becomes downhill, and run the selector. It would be pretty fiddly to get things looking right however.