Some of the most interesting signs birds and animals leave are not tracks, but feeding sign. Trees seem too big to be "prey" for critters, but I've seen some pretty cool "tree tracks".
In the top photo, taken at Frenchman's Coulee, a porcupine has been taking chunks out of the bark. I've yet to see a complete and clear porcupine track - the ones I've seen have been in loose sand, and not at all clear. However, the clear incisor marks on this tree indicate that one (or more) lives nearby. There's likely a den in the rocks somewhere along the basalt cliffs. It would be worth spending a day there looking for the piles of scat that pour out of a porcupine den...a nice fall or early winter trip. The east side sun will be brutal there in the summer months.
The second photo shows the work of the red-breasted sapsucker...this bird drills holes in the bark to collect sap which then traps insects. I see lots of sapsucker sign here in Washington...On my walk to work -about a mile and a half - I know of 20 trees just along the street that have been worked by these birds...I even saw one once!