You don't have to go to bedrock to get a good low water crossing. Get down to something halfway hard (be sure and go a couple to three feet deeper than the creek bed), then put a couple feet of rip-rap rock in there, walk it in with a dozer, then fill the voids with oversize rock, (3"/5" rock). Walk that in also. Top that with whatever you want and you'll have a great crossing. I have several on one of my places that held up log trucks just a few weeks ago. It sounds harder than it is. Initial expense may be more than a culvert, but you're not likely to ever have to worry with it again. Just don't build up higher than the normal creek bottom and you're good. These work especially well in situations where a heavy rain gets the creeks out of the banks for a little while and then runs off. Most places culverts just won't carry that runoff. I've put in lots of culverts in fifty years doing oilfield construction, and culverts are a pain in the butt !