I also can’t find an option to download all of the United States packs at once for eBird mobile. I’m guessing they have it set up that way so that you just have the individual packs available for whatever state you are currently in. You wouldn’t want to be in Idaho and have all ~1,000 possible species in the U.S. show up on your expected list in eBird! 😀  Thankfully, we only have a few hundred species that show up on the Idaho bird pack. 😀

I’m sorry that isn’t more helpful, but there doesn’t appear to be a way to download the whole U.S.; you just have to download each state before you visit it. 🙁

I’m glad you asked this question, because it prompted me to download the state packs for each state that I will be going through on an upcoming road trip! 😀

Have a great week! 😀

—
Aidan Lorenz
Caldwell