So is it possible for parts of the US that are actually thriving with nature ect and are normal?
Yes and No.
Are there areas that are thriving with nature, yes, and you don't need a GECK to get there - Zion, etc.
Are there areas that are "normal"? No. The Biosphere has irrevocably changed, many creatures have become exitnct, others have risen to take their place, (not just through FEV and Radiation, but normal natural selection and introduction of foriegn species as they leave farms and zoos).
For a view as to what using a GECK looks like, I'd recommend a visit to Vault City (ie- play Fallout 2).