Moved from Pinions.
ID confirmed by David Wagner.

Moved from Butterflies and Moths.

I got a very informative response from Sam Jaffe: "For a few weeks every spring winter moth caterpillars and various oak sawflies gather in the thousands on some wooden parking lot barriers beneath a stand of pin oak in my neighborhood. It's quite an interesting scene as birds, spiders, centipedes, carabid beetles and many other predators quickly focus in on the area. Two years ago I noticed that various noctuid caterpillars were also cruising the barriers alongside the wintermoths and I was astounded to see that they were joining in on the feast, grabbing and devouring neighboring larva at a surprising rate. I collected and raised both the Ashen Pinion, Lithophane antennata, and the Shivering Pinion, Lithophane querquera, but I believe other Lithophane may have been present at the scene as well.

Your caterpillar is a close match to the Lithophane antennata I have raised (spiracular stripe encompasing relatively unmarked spiracles, extremely sharp margined dorsal spotting organized roughly into three subdorsal stripes, unbroken mid dorsal stripe...) - so thats my vote. However, David Wagner mentions in his guide that L. laticinerea has a very similar caterpillar but with a broader middorsal stripe and more organized subdorsal striping, so there are look-alikes. I'll copy this whole series to him and see if he might offer a more educated opinion on pinions.

Here is an image of one of my L. antennata devouring wintermoth: http://www.pbase.com/spjaffe/image/112948427"

any lateral images? L. unimoda is similar, Wagner pg 408, but there are plenty o' Lithophane!