Caterpillars and adults of some of the geometrids can be difficult to identify. The caterpillars of N. californiaria have a little lateral (i.e. not dorsal, not ventral) bump on each side of the second abdominal segment. This alone may not uniquely identify the insect, but it may be a help. The caterpillar feeds mainly on Douglas Fir Pseudotsuga menziesii, but I have also found and reared it on Bitter Cherry Prunus emarginata and on Snowberry Symphoricarpos alba. It overwinters as a young caterpillar, occasionally nibbling if the weather is mild. The several cross-lines on the adult's wings are frustratingly similar to those of other species. However, the cross-line across the middle of the hind wing is bicoloured, being dark on the edge towards the base of the wing and light on the edge towards the outer margin of the wing. Again, this may not be unique to the species, but it may be a help.