NO! Use soil.

Thanks Yardvaark for the response. Just curious - is there a specific reason to do soil, even if we plan to do soil on top of whatever base we put down? I'm just wondering if the soil will really compact enough if the area is 3-4 feet deep. ?

Thanks!

Use soil that is of the same makeup as that which surrounds it at the same elevation ... common, clean fill ...Not a fluffy, water-holding planting mix like you might use for the topmost layer. Compact in thin (a few inches thick) layers as you backfill.

A big pocket of road base would be unpleasant to meet up with in the future should you ever need to dig in the area for any reason. And because it's porous even when compacted, it can collect water. Surrounded on all sides by less permeable materials, it could create a "bowl" effect.

Excellent input and advice. Thanks!!