Found this on a sphagnum mat under some larch which is noted as one of the larval foods for this species. Either I accidentally knocked it out of the tree or it found its own way down looking for a place to pupate. The black circles, the red spiracles, colors of the stripes and horn match descriptions and/or photos at these sites:
Caterpillars of Eastern Forests
Bill Oehlke
Forest Pests

Formerly Sphinx gordius poecila, now apparently elevated to species status as Sphinx poecila

The moss is Sphagnum magellanicum.