Hey! I'm not technically a historian but thought the question could be answered with a bit of general biology from my background. Salt is a massively common compound on earth, obviously in the oceans but also as a mineral in the ground. Whilst it's not essential for all plant life it is still exceptionally common for many biological processes and is vital for most animal if not all animal life. The required amounts of sodium for humans to survive are incredibly low (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5098396/), even the healthy amounts are low as your body is exceptionally good at holding onto salts as the way kidneys work means that salt can only really be lost extensively when you're drinking vast amounts of water with no food intake. Regardless of what they were eating, the chances are they were getting enough sodium from any nuts, vegetables or fruit they could have eaten, looking at some examples of sodium content of modern foods gives you a good indicator of how hard it is to not get enough salt (https://www.ncbi.nlm.nih.gov/books/NBK133307/). Realistically, if they were struggling from salt deficiency, they were likely suffering from much much worse deficiencies first!

Do you mean because of the distance to the sea?

Main sources of salt in pre-columbian North America would be salt springs and salt lakes and coastal estuaries. The first two being found inland as well. They could also extract salt from salty soil and sand, or the ashes of salt plants.

Some further reading from previous answers:

https://www.reddit.com/r/AskHistorians/comments/3kwkzl/was_there_a_salt_trade_amongst_north_american/ https://www.reddit.com/r/AskHistorians/comments/aad3zj/where_did_native_americans_and_other_early/ https://www.reddit.com/r/AskHistorians/comments/42446t/did_midwest_native_americans_produce_salt/ https://www.crt.state.la.us/dataprojects/archaeology/virtualbooks/SALT/hist.htm