I just got a USA tourist visa and I'm going to Mexico soon. I would like to know if I can cross the border to go to the USA (California), knowing that I have stated in my DS-160 form that I intended to go to New York. Note that my question is about entering the USA not Mexico.
I believe you will not have any issue. You could apply for a Visa without any plan.
Q: Is it mandatory to have a specific trip (itinerary) planned to get visitor visa? A: No, you can apply even if you have no definite plan to immediately go on trip to U.S. You may intend to go some later date too. But if you are given 6 months visa, you have to go to U.S. within next 6 months, else it will expire and you will have to apply for new visa. If you get 10 years visa, it is not mandatory to go to U.S. within a specified time period. You can go to the U. S. anytime within next 10 years.