I was also confused about how membership and clubs worked and this is what I found out.
(Disclaimer: If anyone notices anything incorrect, please let me know).
To run at El Mirage (the lakes) you must be an SCTA member.
To be an SCTA member, you must be a member of one of the twelve affiliated clubs.
Also, you
can run as a "
Guest" two times per year - no points, no record and no trophy.
You will receive a time slip though.
If you think you will race more than a couple of times, it is less expensive to join a club though.
Two meets as Guest at $150 each = $300 dollars
Club dues $130 per year + $30 dollars each meet to race
Note: club dues vary from club to club. To join one of the twelve affiliated clubs, you "usually" have to find a member who will sponsor you, go to some meetings, show an active interest and convince them that you have something to contribute to the club and finally, to be voted "in" as a member.
To run at Bonneville you only have to be a BNI member (purchase a yearly membership),
which gives you the right to participate in any of the Bonneville Salt Flat events sanctioned by the SCTA.
Good luck,