Ask HN: How do you file estimated quarterly taxes (USA)

For California state you do https://www.ftb.ca.gov/pay/index.html

It's a payment, not a filing. Go through the payment links and you'll see that you can select 'estimated tax' as the reason for payment

I'd suggest checking with your accountant, to make sure that you're doing it right. Just say hey here's what I'm planning to do, these amounts, on these dates, using these links, does that look right.

Note that depending on your setup you might need to do multiple. E.g. I do quarterly personal estimated IRS payments, personal estimated FTB payments, and corporate estimated FTB payments.