This is a female eastern tiger swallowtail butterfly (Papilio glaucus), by far the most common large butterfly that we have in our garden. The males and females are easily distinguished by the blue on their hindwings, as seen in this photo.
There was a little delay in getting this picture up on my server. I’ve been approaching capacity on the 3TB drive (which is really only 2.7TB) that has most of my photos on it and as I was uploading today’s batch of photos, I reached it. I ordered a new, 5TB drive (which is really only 4.4 TB). I installed it on Monday (8/10) and then spent about 24 hours copying everything to that. It’s now up and running (as I write this on 8/12) and I’m back in business.