How much wilderness land remains in the lower 48?

What percentage of the land lies outside of agricultural and urban areas?



I am a regular subscriber to Nat'l Geographic and am fascinated by those areas which remain 'untouched' by man (parts of New Guinea, Amazon, Siberia, Mongolia).



I've travelled cross-country in the US and have come to realize how blessed we are to have such a humongous country. Much of the land though is paved or covered by farms - hence the above question.How much wilderness land remains in the lower 48?
I don't know if you can consider any land in the lower 48 as being completely untouched land. Even places like Yellowstone and other protected places have paved foot paths for hiking or limited roads for driving. It would be difficult to find any large area of true wilderness.