What Airport ?

At LAX there is a 7-11 when you come out of immigration at Tom Bradley terminal and "maybe" it has sim cards, but selection will probably not be big

and check if there are other ways to get 70 miles , at LAX there are full size buses to many areas and once you get close to your destination you can call Uber for the last few miles ,

if I was an Uber driver I would not want to go 70 miles away from my base , but then yu might find someone that just dropped off a fare at te airport and your area is his Home base,

good luck