Instars uncertain, but approximately 5 to 8.

Based on location this should be A. zephyria; however, the larvae are grayer and just a bit different in pattern than the ones from further south and east. They actually look a lot like larvae of A. cecrops (likely the same species) from Arizona. I haven't seen adults from the Jemez area yet, so will be anxious to see what these turn into. I'm calling them A. zephyria for now, because that's what is supposed to be there. A few were found with A. io larvae (which was abundant) on Salix exigua, and two were found on Robinia neomexicana, but in a couple of hours hiking many hundred were seen on Quercus grisea, Q. gambelii and particularly on Q. undulata. They have eaten several species of Oak in captivity (including both Red ane White group Oaks), and have also eaten Redbud enthusiastically. They will nibble on Ulmus pumila, Salix exigua, Robinia species, and grasses when the Oaks run out, but don't seem fond of them (even though they were found wild on two of these plants). I'm sure they will take many other plants as well.

Sorry the focus isn't perfect, but I figured they were good enough to be of some value.

follow-up - May 27, 2009:
Adults have been emerging from these since about February, and wild adults are now flying in the area the caterpillars were found (Jemez Springs, La Cueva, Los Alamos, etc.). They are actually Automeris cecrops pamina, apparently making for one heck of a range extension. A. zephyria, with normal bright yellow-green larvae were abundant in the same habitat, but in mountains to the east side of the Rio Grande last summer too, making 2008 the "year of the Automeris" in New Mexico, and apparently the adults are going to be very abundant this spring for act two. So far, apparently, nobody has found A. cecrops and A. cecrops in the same location. I expect they are the same species, but it will be interesting to eventually (hopefully) learn more. It could be that the Rio Grande valley is a barrier that they don't cross, but the things can certainly fly far enough to cross the valley, so it seems unlikely. Also, so far, the grayish larvae and bright green larvae seem to constantly belong to A. cecrops and A. zephyria respectively.

Adult photos soon.