hagakure said:

There are 350,000 private homes and 34,000 hotels rooms in San Francisco and a fair deal of them are safe and free from paranoia inducing stimuli. People have been beaten, robbed, raped, and murdered in some of the parks inside the city. Parks outside of the city may be patrolled by cops who can be way less tolerant of drug culture, and, if you are charged with a crime, you will find yourself under the the jurisdiction of a court which is way more strict than San Francisco Superior. There are federal park police in and around San Francisco; they are people who may come from far less tolerant parts of the country and they'll have you in federal court if they can bust you for anything.
I have had plenty of great experiences tripping in this city, a city about which, as indicated by your post, you know very little. Make friends with some real San Franciscans and you might find a place or two that would be suitable for tripping shrooms, LSD, or even for cheesing your f-ing balls off.

---