With the ESTA visa-waiver for the US, what if you have a reason to need more than 90 days?

So I was looking at some long distance hiking trails in the US - the Pacific Crest and the Appalachian. Both require 5-7 months to hike the whole thing.

This is fine for locals, but what about internationals needing that long to do it, when we can only get a 90 day visa?

I figure there's 3 possible outcomes:

either there's a way to extend it,
or you have to fly out and back in again (breaking your continuous walk :()
or there's no way to do it, which would be disappointing.

Any solutions?

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Can I stay more than 90 days with ESTA?

If you plan to stay longer than 90 days, you must obtain a visa at the nearest U.S. Embassy or Consulate. If you obtain a new passport or change your name, gender or country of citizenship, you will be required to apply for a new travel authorization.

How can I stay more than 90 days in the US?

You must apply for a visa (B2 visa) if you want to stay in the U.S. for more than 90 days, no matter what the reason. You must apply for a visa (B1 visa) if you are traveling to the U.S. for employment or business purposes involving remuneration, even if not staying longer than 90 days.

How long do you have to leave the US before returning on an ESTA?

Therefore, the length of time of your total stay, including the short trip, must be 90 days or less.

How do I extend my stay in USA on visa waiver program?

To request this extension of stay, you should schedule an InfoPass appointment with a USCIS officer using USCIS' website, uscis.gov. At this appointment, you should provide documentation and any other evidence to the USCIS officer to support your need to extend your Visa Waiver stay.

Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.

Images: Molly Champion, cottonbro, RODNAE Productions, Elina Fairytale