It's a faded compton's tortoiseshell - beautiful!
Looking at your picture, you can sure see how closely related the tortoiseshells are to question marks.
MissSherry

Thanks so much for the ID! Are the males more brightly colored than females?

I don't know, they don't occur here. The individual in the picture is faded from age, and that happens to both male and female butterflies.
That butterfly was gorgeous when it first emerged!
MissSherry

Thanks again! :-)