Yup! most mini / kart tracks are pretty informal. Just show up. Either pay your track day fee and sign liability waiver at the gate, or office.
Last time I attended Infineon, cost is $60 (full day), $40 for half day.
Dixon and Atwater, $40
Stockton - scheduled track day event, $40 non-members, $30 members. Non-scheduled track day(s), $30 (typically, but subject to change). To become a Stockton Member, contact Allen for pricing.
If you have a FB acct., join the NorCal Mini Racers group page to keep informed of local events - Stockton, Atwater, and Dixon. For Infineon, you'll have to rely on their Web page - Moto's only typically on Mondays and Thursdays
In the case you had never attended a Mini-moto track day, and or a new rider, here is some important general info;
Mini-Moto Open Track Day and Race Series Info