You don't join the SCTA to race at Bonneville, sort of. You need to be a member of BNI, though. You should be able to join SCTA if you really want to do so -- but all of the clubs are on the west coast, and many have requirements that might be hard for you to fulfill (like volunteer duty at El Mirage).
Now -- is there a BNI -joining form in the book? I don't think so. . . SCTA members are automatically BNI members.