I didn't mention that S. hesperis can be silvered as well as un-silvered (depends a lot on where found, but in some areas they can be mixed in one population as well. However, S. atlantis is always silvered.

Assuming the light spots on the underside are not silvered (as they appear to not be in this photo) then this is definitely S. hesperis.

I think I am correct, but I may have moved this to the species prematurely, and I wonder if you have any other photos that would show either side (particularly the under side) more clearly.

S. atlantis from the same area will look very similar, but the underside would probably be less reddish and the light spots would be distinctly silvered, while the upperside would probably have more solidly blackish borders. There is a chance I'm wrong and it really is S. atlantis (the silvering could be obscured by orange showing through from above, and the under side could look more reddish than it is for the same reason). The rather fine dark pattern above, and apparently rather squared front wings are a lot like S. atlantis. Right now the two species are badly confused in Montana, and at present it is often not acknowledged that S. atlantis is even there.

This is definitely not a Great Spangled Fritillary.

Moved from Great Spangled Fritillary.

The Guide could use this sighting if the photo were cropped to enclose just the fritillary.

Moved from ID Request.

great spangled fritillary