Have not shot dogs in that area. If I was going to I'd stop by the BLM and National forest departments to pick up maps of the area. While there they may point you to a couple of spots....Unless they are like the wench at the Casper BLM office
It also pays to stop by the local feed /supply stores or the local cafe's!
Anyway armed with the BLM maps you can start looking for BLM and/or state land that lays in the river/creek bottoms and work out from there.
If your stepping on pine needles your in the wrong place