Unlawful Stop

[Adski]

My question involves search and seizure law in the State of: California. Two friends and I were in my friends car and we drove up to the top of this hill which was a dead end and there was already a cop up there busting someone. So my friend makes a U-turn and the cop puts his hand out in front of him and walks in front of the car and tells us to stop. We stop and roll the window down, we tell him were here for the view and he says he smells the weed so give it up. My friend gives it up and he tickets us all for Possesion of Marijuana. We didnt do anything wrong we were in a registed vehicle nothing wrong at all with the car and we were just going to leave. Can he stop us like that? Isn't that illegal? Can we fight this as an unlawful stop. Thank you for anyones opinion.