Owning promising growth stocks over the long term is a surefire way for you to build your wealth towards a happy retirement.There is a plethora of investment choices in the US market where you can find many growth stocks in various sectors.To build a sturdy growth stock portfolio, you should select companies that possess a robust economic moat and boast strong growth track records.Here are four US stocks you can consider owning for the long term.Palo Alto Networks (NASDAQ: PANW)Palo Alto Networks, or PAN, p ...