A little green crawly thing

This little green caterpillar was slowly crossing the trail when we were on a botanizing hike in West Bragg Creek Natural Area recently. A friend let it crawl on to his hand lens, where I was able to get a somewhat better photo of it before we carefully placed it back down on the ground. Haven't been able to identify it yet - have looked at hundreds of photos of caterpillars but none like this one. Could it be some kind of Duskywing? Or a Sawfly larva?