Where did the United States get its airship helium?

How was the helium used by American airships produced?

For this period, it was chiefly separated from helium-rich natural gas found in the Great Plains.

American helium production depended on unusually concentrated helium within Great Plains natural-gas fields. Industrial separation from that gas gave the United States a massive supply by the standards of the period. An artificial-production process is mentioned without a usable explanation, while extraction was much easier. The historical airship supply therefore came chiefly from separating helium already present in natural gas.