Until we have complete pay transparency, there's only one way to find out whether you're paid fairly, and that's to talk to your coworkers. In the US, the National Labor Relations Act has been protecting employees' rights to collectively bargain for pay and working conditions since 1935. Check your state laws too. The California Equal Pay Act was strengthened in 2015 “making it illegal for employers to prohibit employees from discussing or inquiring about their co-workers’ wages.” California also just passed SB 1162 requiring pay transparency in job listings, which will go into effect in 2023.
You can start by finding a peer who agrees it's worth braving the discomfort because this information is power your employer has, that you both should have too. Then share your base salary, stock, signing bonuses, annual bonuses, and any other benefits you've negotiated. Talk about how they've changed year over year—did you get RSU refreshes? Better bonuses in years where you had great project assignments? Did you ever ask for a raise and how did it go? Document what you find, in a file you own and control.