Should I wait to sell them after I move to WA? Will that help me avoid
the 10% tax that CA imposes?
Ignoring the risk of waiting.
You will have to provide enough proof that California can't claim you are still a resident of their state.
That means don't sell until you have completely severed all ties to the state of California. Get a new drivers license, and register to vote. Register your cars in the new state. Close your California bank accounts, and open one at a bank in the new state, and put all your money there. Have all your mail sent to the new state. Don't own, rent, or lease property in the California, get a place in the new state. Don't have your stuff in a California storage facility. Have a job that doesn't connect you to California.
The more connections you still have to California the more likely they can argue that they are allowed to tax your income.