About all the legalities involved...just about anything is illegal if you look at it the wrong way. I don't think you knowingly did anything wrong, and I'm sure you won't keep it long. I'll bet you're one of those good people who want the best for the bird and will give it a successful next step in its bird life. I don't think you should be the least bit careful of posting this info for us to see, like others have said you should be...
Its a common bird that nobody would miss (or look in your back yard for), you helped it out a bit...its no biggie, and personally-I would have likely done the same.
ANd about the crazy idea of getting a permit to potentially keep this bird...Even if you have permits for animals, that doesn't prevent you from getting harrassed by fish and game and/or raided... my dad's buddy had a few rare falcons and a golden eagle with a degenerative foot disease that required daily ointment and therapy that he had for years, the Fish and game guys never let up on him though he had always had legal permits and finally they raided his house when he was gone one day and took his birds and uthenized them since they couldn't take care of them...and because they didn't want to deal with him wanting them back.... so don't bother with permits.
Everything seems to be protected these days, one of the reasons that the whole west coast is OVERRUN with seals, they're menaces and cause a million problems-including attracting record numbers of great white sharks close into shore!!!, plus cost taxpayers a ton whenever they get "rehabbed" or sink vessels in the harbors... There should be a reasonable goal amount attached to protected species so they don't get more than their fair share of human protection and help... yeesh... good intentions start out allright but later open up a whole can of worms.
oh, and I think that bird is pretty gnarly looking, its feet are so strange!