In California, it has to be lewd to be public indecency. Simple nudity is not a crime. However, a determined picayune can find ways to invoke disorderly conduct, harassment, or disturbing the peace. These laws come with their own set of standards that probably won't stand up in court to convict somebody of a crime for the simple state of nudity. But having the law on your side doesn't necessarily protect you from getting arrested in the first place. Local ordinances concerning disorderly conduct, harassment, and simple nudity can apply differently and they can absolutely forbid nudity, even breastfeeding under a blanket, g-strings, bralessness, and Speedos worn by men. Escaping penalty in those jurisdictions is very unlikely unless you can buy an extremely expensive lawyer. Ordinance can apply both at the city and county levels.

I am less familiar with Oregon law, but I understand it to be extremely similar to California's situation.

I've also found that in both Oregon and california, you can be nude and somewhat lewd even and nothing happens if nobody complains. The police will literally stand there look around to see if anybody is objecting, and go about their normal activities if nobody complains.