How much capital gains tax would be in California for a property that I bought in 1997 for $500,000 and sold today for 1,000,000?

it depends; unless your tax rate is higher than 15% , then 0% if yur tax rate is 25% or higher than then 15% , if the tax rate is 39.6% then it will be 20% on the Long term capital gain

Sorry it is my bad as I gave you federal LTCG rate ; for your CA long term capital gain tax rate, you need to contact CA tax svc;
https://www.ftb.ca.gov/forms/search/index.aspx